The acceleration of the Iranian nuclear program represents a defeat for the Clinton Administration's drive to halt the spread of nuclear technology to Iran.

Iran, like Iraq, was to have been isolated by severe sanctions in a policy described by Administration officials as "dual containment." But senior Administration officials interviewed in Washington said their efforts had failed to halt the flow of nuclear technology to Iran.

The most active center for nuclear weapons research and production is in Bushehr, on the Persian Gulf 470 miles south of the capital, Teheran. It has two reactors under construction, each designed to generate up to 1,300 megawatts of electrical power, about as much as the largest reactors in the United States.

So far the Iranians have done little more than amass nuclear material and some equipment, including a neutron source reactor and an isotope separator. They have yet to build, as the North Koreans did, a nuclear reactor that can be used to develop nuclear weapons.

But the Americans and Israelis worry that if the scheduled building programs proceed, Iran will have all the components needed to build atomic weapons by the decade's end.

A prominent specialist on Iran, Dr. Shahram Chubin of the Graduate Institute for International Studies in Geneva, who is the author of a recent article on the Iranian nuclear weapons program, agrees that the Iranians could have nuclear weapons within five years. But he is less certain that Iran would be a serious threat at that point.

"How will a few weapons that can't be developed very far get them anywhere?" Dr. Chubin said in a telephone interview from Geneva. "Here is a country that can't make its own missiles. It has had a missile program for 10 years and still imports missiles with 1950's technology from North Korea.