Facing tough questions about the Bush administration's proposed deal to aid India's civilian nuclear program, Secretary of State Condoleezza Rice told Congress that she would press New Delhi to back up its stated commitment to stop the spread of nuclear arms.

Rice said she would push India, for example, to conclude an agreement with the International Atomic Energy Agency on safeguarding its civilian nuclear plants as a way of reassuring lawmakers, but that she could not guarantee that India would do so before Congress could vote on the deal.

"What I can guarantee you is that we will make every effort to push that process forward," Rice told Senator John Kerry, Democrat of Massachusetts, at a Senate Foreign Relations Committee hearing Wednesday.

In a sign that the proposal may have more support in Congress than some of its opponents had suggested, Kerry said he would probably support the deal, especially if the administration could provide the assurances he sought.

A similar tentative endorsement came from another influential lawmaker, Senator Joseph Biden of Delaware, the ranking Democrat on the committee.

The qualified support from Biden and Kerry elated administration officials, who said they now believed that they could build on the momentum from the hearings to try for a vote as early as May or June. Committee officials said a vote might be delayed until July, however.

Rice also testified before the House international relations committee, where the proposal got even more bipartisan support. That was considered significant because of the earlier vociferous criticism of some Democrats and misgivings expressed by the chairman, Representative Henry Hyde, Republican of Illinois. An aide said that Hyde had not endorsed the plan but had not ruled out doing so.

Rice said the United States was also pressing India to join a treaty to block exports of fissile material for use in making a nuclear weapon and international conventions governing the transport of chemical weapons and nuclear technology.

The administration has in effect proposed letting India bypass the Nuclear Nonproliferation Treaty, which it has not signed. The deal would permit the Indian authorities to receive vital help for their civilian nuclear program, including uranium for fuel, while being allowed to retain or increase their arsenal of nuclear weapons.

Many experts on proliferation have been critical of the arrangement, saying it rewards India for defying the basic underlying philosophy of the treaty, which is that only countries that forswear nuclear arms can get help with their nuclear energy needs.

But there are also independent experts who favor the deal because it puts most of India's reactors under civilian auspices and therefore under international inspection. About a third would stay under military control and therefore beyond inspection by the international atomic agency.

Several Democratic senators, including Barbara Boxer of California and Russell Feingold of Wisconsin, said at the hearing that India did not deserve the deal, despite their desire to improve relations.

Other lawmakers noted great support for India as an emerging power that could serve as a counterweight to China.

Rice sought to play up the importance of improving ties with India but also warned bluntly that if the treaty negotiated by President George W. Bush failed, bilateral relations would suffer dramatically and broader U.S. interests in Asia would suffer as well.

Lawmakers expressed concern that the proposed deal curbed the power of Congress by leaving India exempt from the Nuclear Nonproliferation Treaty, rather than getting India to join and then allowing a waiver, which could be reviewed annually and approved by Congress if India met its commitments.

A senior State Department official, who was granted anonymity because he was not authorized to speak for the record about the administration's tactics, said afterward that the White House would be amenable to having Congress attach legislative requirements to the deal, as long as that did not require a renegotiation.

An Indian official said India could accept such an arrangement as long as it required India to do things that it had already agreed to do.