Despite the dogged resistance of some athletes, U.S. Olympic Committee (USOC) delegates appear certain to vote Saturday to accept President Carter's demand that no Americans compete in this summer's Olympic Games in Moscow.

Even though many of the 341 voting members of the USOC House of Delegates are resentful of what they consider threats and strongarm tactics by the Carter administration to enforce the boycott demand, momentum has built steadily over the past two days for a vote against sending a team to Moscow.

Delegates have been told repeatedly, in briefings by top administration officials and in telegrams from Carter, that U.S. participation in the wake of the Soviet invasion of Afghanistan would be inconsistent with the national interest and security.

Carter said Thursday that he would take legal action if necessary to prevent American athletes from competing in Moscow.

Vice President Mondale will restate the administration's case at the start of the House of Delegates meeting. Following his address, which will be broadcast nationally by the Public Broadcasting Service and National Public Radio, the delegates will go into closed session.

Mondale, on arrival at Peterson Air Force Base here tonight, called the boycott decision "critical to the future of our whole nation," and said he was confident the USOC's decision "will reflect . . . the American consensus on the Moscow Games."

He said that a USOC vote against sending a team to Moscow would be a signal to other western and Third World nations to follow the same course. "We are confident that most of the major noncommunist sporting nations will not participate in these Olympics but nothing would help us more in achieving that desirable result than a favorable . . . vote by the committee here," Mondale said.

Tonight, a group of athletes drafted an alternative resolution for the House of Delegates in an effort to keep open the possibility of going to the Games. At an earlier news conference, they indicated that a legal challenge is likely if the USOC votes to boycott the Games.

Anita DeFrantz, an Olympic rower and attorney, said the athletes would undoubtedly take the USOC to court and argue that it was in violation of its own constitution and the Amateur Sports Act of 1978 (Public Law 95-606), which charges the USOC with the responsibility of preparing and sending an American team to the Olympics.

However, the ahtletes admitted that this would most likely be a legalistic exercise in futility, since the president probably could invoke authority under the Emergency Powers Act to preclude athletes from going to Moscow, and Congress could amend the Amateur Sports Act.

DeFrantz said that the American Civil Liberties Union and other legal groups have expressed interest in the athletes' cause, and may test Carter's authority to bar travel to the Soviet Union on grounds that this is an abrogation.

Nevertheless, the immediate question of how the House of Delegates will vote Saturday seems to have become a foregone conclusion. "It is my personal view that the die has been cast," said USOC legal councelor Patrick Sullivan. "I do not believe the USOC will send a team to Moscow. The power of the president is too great."

Convinced that the president will not soften his position that a boycott would be an effective and necessary rebuke to the Soviet Union for its aggression, the USOC leadership appears to have abandoned its earlier determination to defer a decision until May 24, entry deadline for the Moscow games.

Discussions among USOC officers and influential delegates today seemed to center instead on how the USOC could best utilize a vote backing the president -- "how to capitulate on the most advantageous terms," as one officer put it.

In exchange for its support of the president's boycott demand, the USOC would like assurances of federal assistance, including the $4 million appropriation that the White House has requested in its 1980 budget and a promise of tax exemptions for nonprofit sports organizations within the USOC family.

The USOC also is seeking statements of support from the president which could help revive the organization's fund-raising efforts. USOC contributions have fallen precipitously since Carter first proposed a Moscow boycott on Jan. 4, and the organization is facing a projected $7 million budget deficit by the end of the year.

Asked if the administration had agreed to give financial support to the USOC if on Saturday it rejects the invitation to Moscow, Mondale said: "There is absolutely no deal whatsoever. We have always been strong supporters of the Olympics, we are strong supporters of the U.S. Olympic Committee, and we'd be glad to help in any way we could."

Delegate Harold O. Zimman of Marblehead, Mass., a reliable bellwether of USOC opinion, said today: "Unhappily, the USOC is going to vote for the first time in its history not to accept an invitation to participate in the Olympic games. I don't hear very many people saying 'let's fight this.' I think the vote could be near unanimous."