The Bush administration has been unable to win congressional support for its plan to continue giving U.S. aid to Pakistan, in part because of new intelligence information indicating that Pakistan may have developed a nuclear weapon, according to U.S. officials and key legislators.

Senate Democratic leaders and some Republicans say they are willing to place in jeopardy a Washington-Islamabad partnership of more than 30 years' standing by cutting off roughly $600 million a year in economic and military aid in order to pursue U.S. policies against nuclear weapons proliferation.

Secretary of State James A. Baker III yesterday informed Pakistani Foreign Minister Sahabzada Yaqub-Khan of the congressional rebuff and told him in a meeting at the State Department that further aid would be impossible unless Islamabad provided convincing new evidence that no such "nuclear device" exists.

While Yaqub-Khan reiterated past Pakistan assurances of peaceful aims for the nuclear program, his pledges to make new disclosures fell somewhat short of the administration's demands, a senior administration official said. A similar request for more Pakistani disclosures about its program, made over the weekend by U.S. ambassador to Pakistan Robert Oakley, was spurned by interim Prime Minister Ghulam Mustafa Jatoi, other officials said.

The Pakistanis "are not home free" and no final U.S. decision on the aid has been made, the senior official said. Others said senior administration officials met at the White House yesterday to discuss the impasse, but did not come up with a new strategy for overcoming congressional opposition.

A Republican source said there was "considerable panic" within the Department of Defense over the sudden termination of assistance to a Moslem country that has been strongly supportive of the Western and Arab campaign against Iraq's invasion of Kuwait.

Deputy Assistant Secretary of Defense Henry Sokolski told the Senate Governmental Affairs Committee yesterday the administration was "reviewing" whether to try to change the law tying aid to a curtailment of the Pakistani nuclear effort.

Since Oct. 1, when Bush failed to meet a congressional demand for certification that Pakistan does not possess a nuclear device, all new economic and military aid to Pakistan has been legally blocked, officials said. Existing military assistance has been halted in mid-stream, but existing economic aid has been allowed to continue under the administration's interpretation of a 1985 law designed to halt the Pakistani effort.

Military aid to Pakistan that was authorized for fiscal 1990 totaled $352 million, while economic aid totaled $230 million. Pakistan is the third largest recipient of U.S. foreign aid after Israel and Egypt.

Several weeks ago, administration officials believed they might secure a temporary legislative suspension of the requirement for Bush's certification on the status of the Pakistani nuclear program. They told key legislators that no penalties should be imposed until an assessment could be made of the impact of the Oct. 24 presidential elections in Pakistan.

Administration officials have also expressed concern that a cutoff of Pakistani aid would be seen as a definitive statement of the existence of a nuclear device in that country, which in turn would provoke new concerns and spur enhanced nuclear weapons development in neighboring India, which exploded a nuclear device in 1974.

But seven senior Senate Democrats, including Majority Leader George J. Mitchell (Maine), Majority Whip Alan Cranston (Calif.), Intelligence Committee Chairman David L. Boren (Okla.), Foreign Relations subcommittee chairman Daniel Patrick Moynihan (N.Y.), and Governmental Affairs Committee Chairman John Glenn (Ohio), decided in a recent meeting to oppose any suspension of the certification requirement, sources said.

"Although there are real differences between Pakistan and Iraq, the gulf crisis makes it clear that we must cut off Pakistani aid if we want to be vigilant and follow the fundamental purpose of our laws," said Sen. Joseph R. Biden Jr. (D-Del.).

"If we lower our standards again, who is going to take the standard seriously?," said Sen. William S. Cohen (R-Maine).

In one signal of congressional sentiment, the Senate Appropriations subcommittee on foreign operations last week declined to earmark any new foreign aid for Pakistan, forcing the country into direct competition with other nations for a share of the total aid pool. None of its Republican members proposed the certification suspension sought by Bush.

Staff writer David Hoffman contributed to this report.