Local developer Gopal Kris Kapoor is backing a New Jersey company’s plans to build a $200 million outpatient cancer treatment center and hotel complex in Allentown that offers a type of radiation therapy available at only three major medical centers in the country.

The company, Proton Therapy Inc. of Marlton, N.J., is a for-profit business named after the type of cancer treatment now offered only at university medical centers in California, Indiana and Massachusetts and at select sites in Japan and Europe.

Proton therapy’s potential advantage over conventional radiation therapy is that it can deliver higher doses of radiation with more precision and fewer side effects to cancers that are slow-growing or risky to treat, such as those in the prostate, head and neck.

The sites under consideration were not disclosed, but an economic development official said the lots are privately owned and outside center city.

If built, the complex could create more than 200 jobs. It would be the first privately owned and operated free-standing proton therapy center in the United States.

‘‘This could put the Lehigh Valley on the map of the world for cancer treatment,’’ said Kapoor, noting that South America and many countries elsewhere have no proton therapy centers.

Kapoor, who lives in Hanover Township, Northampton County, once owned the Fuller Co., a worldwide supplier of heavy equipment for the cement industry. He made millions on the sale of the Catasauqua company in 1989 and on subsequent land development.

Although Proton principals have been discussing the plans privately with local government, economic development and hospital officials for months, it could be three years or more before patients receive cancer-zapping treatments at the center.

Such a major undertaking involves state and local approvals, considerable capital and complex construction that leave the project open to questions about cost, need and means of developing it privately.

‘‘I don’t know how they can do it without a hospital affiliation,’’ which presumably has more resources and medical expertise at hand, said Len Arzt, executive director of the National Association for Proton Therapy in Silver Spring, Md. ‘‘There are a lot of ‘ifs’ out there, but more power to them.’‘

Constrained by cost, the Hospital of the University of Pennsylvania has been trying to open a proton therapy center in Philadelphia for 10 years. And cancer specialists providing traditional radiation therapy in the Lehigh Valley question the need and expense of added technology and treatments.

But Kapoor, Proton’s vice chairman, and other company directors are confident they have the money, expertise and support to break ground by 2006.

Proton applied to Pennsylvania for $10 million to $15 million in grants or other tax-free incentives, according to Frank Hess of Delanco, N.J., a retired financial adviser and Proton’s secretary/treasurer. If they are granted, he said, Proton could save $6 million on the $80 million equipment and millions more in property taxes.

Yet state assistance is ‘‘not critical’’ for the plans to proceed, Hess said. When construction begins, he said, Proton will have about $40 million in working capital from the private investors on the board and from pension funds and equipment manufacturers that want to invest in the company.

Proton’s chairman is Irv Richter of Cherry Hill, N.J., chairman and chief executive officer of Hill International, one of the largest construction management companies in the country.

For months, Kapoor and other principals have been meeting with and enlisting support for the project from Lehigh County, Allentown, the Allentown School District, state legislators, the state Department of Health and members of the Governor’s Action Team, which seeks to attract businesses and jobs to Pennsylvania.

Allentown Mayor Roy C. Afflerbach wrote a letter to Gov. Ed Rendell on Dec. 16 endorsing the plan as a means of creating jobs, stimulating economic growth and helping to revitalize the city.

City officials are ready to help Proton find an appropriate location and cut through bureaucracy for zoning and planning approvals, Afflerbach said.

‘‘We are assuring them of fast-track cooperation to the extent the administration is able,’’ he said.

A prostate cancer survivor, Afflerbach knows the Kapoor family. Kapoor’s son-in-law, Abe Atiyeh, gave Afflerbach more than $20,000 in cash and services for his 2001 mayoral campaign, and Afflerbach appeared in a commercial for Atiyeh’s assisted living centers for seniors.

The city and county as well as the Lehigh Valley Economic Development Corp. have been courting Proton for more than a year, said Robert J. Osborn, executive director of the Allentown Economic Development Corp.

‘‘They are the real deal,’’ Osborn said. ‘‘This is big business. These are not just some guys with an idea. We were fortunate to be included. -  They were originally going to Philadelphia.’‘

They also looked at Bethlehem, Osborn said.

Proton chose the Lehigh Valley because of its proximity to major highways, interstates and an international airport, said Nathan Kline of Allentown, a retired businessman and member of the AEDC and the Proton advisory board.

Osborn and Afflerbach said the city plans to help Proton get the $10 million to $15 million in state economic development aid that company officials say would pay for infrastructure improvements such as roads, sewers and other utilities at any of the sites under consideration.

Pete Reinke of Forks Township, a regional director for the Governor’s Action Team, confirmed he is working with Proton officials but said he couldn’t comment further on the potential for state assistance.

AEDC would serve as developer for the project to facilitate state assistance, Osborn said. The aid could come in the form of loans and grants, tax abatement programs and special financing arrangements, according to Afflerbach.

Kapoor would not disclose the exact locations under consideration, but Osborn said the properties are privately owned and outside center city. Proton’s Hess said one of the city properties is owned by a member of the company’s board.

Kapoor owns and has been trying to develop a 12.6-acre property on Union Boulevard that’s the site of the defunct Boulevard Drive-in. He tried to attract Lucent Technologies there to build a $25 million office and laboratory and a hockey arena. A proposal still on the books calls for 188 townhouses on 22 acres at the closed drive-in and neighboring tracts, provided they can be rezoned.

Hess said he first heard about proton therapy from a friend with prostate cancer who could not afford to fly to Loma Linda, Calif., for treatment. In 1990, the Loma Linda University Medical Center was the first medical center in the country to set up a treatment center for proton therapy outside of experimental research.

After researching the potential advantages, Hess said he was sold. He, Richter and other business leaders founded Proton and incorporated it in April 2002.

Because there are fewer than a dozen proton centers around the globe, the proposed ‘‘Lehigh Valley Proton Center’’ would draw patients from a 250- to 350-mile radius. A 120-suite hotel would house out-of-town patients and family members in between the minutes-long treatments delivered over days and weeks.

The biggest obstacle would be keeping up with demand, Hess predicted. The center would have four treatment rooms capable of treating 2,400 patients a year. Yet there are 40,000 new cases of prostate cancer diagnosed each year in the region, he estimated.

‘‘And that doesn’t include brain tumors, benign and malignant, or spinal tumors,’’ Hess said. ‘‘Protocols are being established for breast, lung and liver cancers. And the possibility exists that proton therapy can help people with Parkinson’s disease and epilepsy.’‘

However, local cancer specialists, who provide conventional radiation therapy and refer patients elsewhere for proton therapy, cast a more cautious eye to the need, expense and capabilities of proton therapy.

Dr. Victor Risch, who is chairman of radiation oncology at Lehigh Valley Hospital and Health Network, said that while proton beam therapy is a viable treatment option, it represents ‘‘only an incremental benefit to only a very small percentage of cancer patients in the Lehigh Valley.

‘‘Given the enormous expense of the project and the fact that health care needs affect many more areas than cancer care alone,’’ Risch said, hospitals in Allentown would rather see limited resources go to existing nonprofit hospitals for broader community needs.

Dr. Lee Riley, medical director of the cancer center at St. Luke’s Hospital & Health Network, said, ‘‘I’d love to have one in the Valley, but it fits a small niche.’‘

Proton officials don’t view local hospitals or the University of Pennsylvania Hospital as competitors.

Proton therapy will complement current cancer treatments at area hospitals and doctors’ offices, Hess said. And the fact Penn plans to open a center ‘‘demonstrates the value of proton therapy.’’ It will help promote the Lehigh Valley center’s services, he added.

Besides Loma Linda, where 150 patients receive treatment daily, proton therapy is offered at the Northeast Proton Center at Massachusetts General Hospital in Boston and the Midwest Proton Radiotherapy Institute at Indiana University, Bloomington, Ind. The MD Anderson Center in Houston and the Shand Institute in Jacksonville, Fla., anticipate opening centers in 2006.

The proposed local center would be three stories high, with one or two floors underground, Hess said. Each doughnut-shaped treatment ‘‘gantry’’ would weigh 200 tons, he added, and must be supported by 10 feet of concrete flooring and equally thick concrete walls separating treatment rooms.

About 100,000 square feet of space is needed for the medical center, he said, and about 10 acres for the lot, including the hotel and parking.

Hess said Proton centers take three years to build, half the time for construction and the other half for installation of equipment.

Pennsylvania’s Department of Environmental Protection, which licenses and regulates machines that emit potentially harmful radiation, has yet to receive an application or proposal for a proton center. It’s not a long process, said DEP spokesman Ron Ruman.