The Carter administration, in a last-minute effort to avert congressional defeat on a major foreign policy issue, has agreed to new restrictions on the controversial shipment of nuclear fuel in India.

Secretary of State Edmund S. Muskie will personally deliver a letter to the Senate Foreign Relations Committee this morning outlining the concessions. Muskie will lobby the senator's in private and testify in public just before the committee votes in late morning on the hotly contested issue.

The House Foreign Affairs Committee, meanwhile, will be voting this morning on the nuclear fuel issue on the other side of Capitol Hill. The administration has all but given up hope of staving off defeat in that forum.

Both houses of Congress would have to vote resolutions of disapproval in order to block the shipment of 38 tons of enriched uranium to India as proposed by President Carter. Administration officials expressed cautious optimism that the Muskie letter, plus intense lobbying by a variety of high officials, will convince the Senate to back the White House position and thus allow the fuel to go.

The stakes in the battle, going far beyond Carter's congressional clout in the midst of his reelection campaign, involve the future of the U.S. effort to halt the spread of nuclear weapons and the future of U.S. relations with India and Pakistan.

The fuel shipment is the first to be seriously contested under the 1978 Nuclear Non-Proliferation Act. India, which exploded a nuclear device in 1974, has refused to comply with the act's requirement that all its atomic facilities be placed under international safeguards in order to obtain a continuing flow of nuclear material from the United States.

The administration argues that failure to provide the fuel, the raw material for the Tarapur power reactor, is likely to cause India to consider its past nuclear agreements with the United States to be void, disregard established safeguards on U.S. uranium provided in the past and turn to the Soviet Union for its future fuel. All this, the administration argues, would bring a crisis in Washington-New Delhi relations and set back the cause of nonproliferation.

Congressional opponents argue that allowing the fuel to go would destroy the credibility of the 1978 law and of the U.S. drive to force acceptance of international safeguards on all atomic facilities.

Muskie's letter, in response to a set of proposals from Sen. Frank Church (D-Idaho), the committee chairman, agrees that:

A first shipment of 19 tons of fuel would go immediately but the remaining fuel would not be shipped for about a year.

If India explodes a nuclear device, prepares to explode one or disregards existing safeguards in the meantime, the additional fuel would be stopped.

This would be the last exception to full application of the 1978 non-proliferation act.

Sen. John Glenn (D-Ohio), a leading opponent of the fuel shipment, served notice yesterday that the concessions are unacceptable to him. The sending of any fuel at this time without conditions would signal the world that "a substantive change has occurred in the U.S. commitment to its non-proliferation policy," Glenn said in a statement.

Muskie, who held an unannounced breakfast meeting yesterday with 11 senators on the nuclear question, said in a letter to members of the Senate that he had come to favor the shipment after personal study of the issues, even though he was initially skeptical. He said the matter is "admittedly a close call."