Treasury Secretary James A. Baker III yesterday pledged "a full-court press" by the Reagan administration to get Republican support for $1.3 billion in fiscal 1986 budget authority for the international lending banks, but he conceded he couldn't promise to deliver a majority of the Republican votes in Congress.

Baker also indicated that the administration will support a new program for the World Bank's International Development Association -- which makes subsidized loans to poor countries -- when the present IDA-7 program expires in mid-1987.

Until now, the administration had said only that in view of severe pressures on the budget, it would defer decisions on a new IDA until later in the year. But Baker said yesterday that "IDA-8 negotiations will commence in late 1985 or early 1986, and should be completed in time for IDA to begin making commitments in July 1987."

Baker testified before the House Appropriations subcommittee on foreign operations that deals with the World Bank, the Inter-American Development Bank, the Asian Development Bank and other multilateral development banks (MDBs).

Despite Baker's endorsement and a declaration of "the importance to the United States as a nation to fulfill its international commitments," he was told by subcommittee Chairman David R. Obey (D-Wis.) that the MDBs are "dead" for this session of Congress unless the Republicans produce the needed votes.

"We are prepared to do our duty, but we're not prepared to be punching bags for Little Leaguers on your side of the aisle," Obey said. He noted with sarcasm that the administration "professes to support the appropriations in international circles, but when it comes to the pit, in the arena where the political blood is actually spilled, the administration has not yet been able to deliver.

"There will be no funds for these banks unless there is a Republican majority of votes on the House floor," Obey said. His forecast was repeated by other Democrats on the subcommittee.

The issue of administration support -- or lack of it -- for the MDBs intensified two weeks ago, when Rep. Jack Kemp (R-N.Y.) proposed an amendment to block $237 million in supplemental fiscal 1985 funds for them. When Republicans supported the Kemp proposal rather than the administration request, Obey allowed the Kemp amendment to succeed, by 8 to 3.

House Democrats are sensitized, as Obey told Baker yesterday, by the fact that many of them who supported the administration's 1983 request for funding of the International Monetary Fund were later denounced as radicals and "soft on communism" by the Republican House congressional campaign committee.

A critical test for the administration and the MDBs will come early next week, when the full Appropriations Committee could reverse or let stand the subcommittee vote on the Kemp amendment.

Yesterday, Baker strongly endorsed Obey's demand for bipartisan support and said that "the administration firmly supports the MDBs and their vital role in preserving and enlarging the international economy by providing technical and financial assistance to developing countries."

Of the four Republican members of the subcommittee, only Rep. Mickey Edwards of Oklahoma showed up for yesterday's hearing. He was joined by Silvio O. Conte (Mass.), the ranking Republican on the full committee, who urged Baker to "pull out all the stops" in an effort to get Republican support.

"If you don't get this done in the supplementals, when we get into the 1986 budget, we're in a real crunch," he advised Baker. Referring to the subcommittee vote, Conte observed: "We got clobbered, and clobbered pretty bad. I hope you can work something out."

But Baker, although predicting he could round up "substantial minority support" among Republicans, refused to meet Obey's demand for a majority.

"I can guarantee you one thing: If you don't have a majority, there won't be a majority on our side either," Obey said. "I can count, I've had experience doing that. And the members on my side have made clear to me that they are not going to carry that water alone any more."

Obey suggested that, given the pressure to reduce the federal deficit, the administration should consider reducing its requests for the MDBs by 20 percent, because revenue falls that much short of projected expenditures. But Baker said the $1.3 billion requested for fiscal 1986 represented agreed-upon international commitments.

"I suggest we don't give up before the fight has begun," he told Obey.