The Carter administration apparently has decided to reject a proposal that would allow U.S. athletes to compete in the Moscow Olympics this summer while still protesting the Soviet invasion of Afghanistan.

Asked yesterday if the proposal -- offered Saturday by the Athletes Advisory Council to the U.S. Olympic Committee -- would be rejected, a White House aide said, "Of course. The proposals have been raised by everybody from the beginning and were unacceptable."

The aide, who asked not to be identified, said similar proposals had been discussed and rejected between the invasion and the administration's formal call for a boycott in January.

The aide also said it may be a while before there is a formal rejection of the proposal, which was presented in Arlington Saturday.

Under the council's proposal, U.S. athletes would not take part in opening, closing or medal ceremonies; stay in the Soviet Union except on the day of their event; engage in tourism, or leave the Olympic Village or training areas.

The 47-member council's plan was presented to White House aide Bob Berenson Saturday night, a day after the athletes were told emphatically by President Carter that the United States will not participate in the Games.

"I can't say at this moment what other nations will not go to the Summer Olympics in Moscow," Carter told the council members and other athletes and coaches. "Ours will not go. I say that not with any equivocation. The decision has been made."

Anita DeFrantz, an Olympic rower chosen to speak for the athletes council, said yesterday she still believes the plan would be effective and hopes the athletes will be given a chance to discuss it more fully with administration officials.

DeFrantz and USOC Executive Director F. Don Miller noted that the athletes' proposals were similar to some suggestions made by 16 European national Olympic committees meeting in Brussels last weekend.

Miller, who returned from Brussels yesterday, said several nations were "interested and favorably inclined toward some official protest to the Soviet Union's blatant aggression in Afghanistan."

Representatives of some of the committees mentioned that they might not participate in opening and closing ceremonies while other favored having their athletes march under national Olympic committee flags instead of national flags, Miller said.

There also was substantial support, he added, for having the athletes grouped together by sport rather than by nations in the ceremonies in an effort to deemphasize the nationalistic overtones of recent Olympics.

The national committees have asked for an opportunity to make these suggestions to the International Olympic Committee at an April 21-23 meeting in Lausanne, Switzerland.

In another development yesterday, an Associated Press-NBC News poll showed that Americans still favor a U.S. boycott of the Games.

Of the 1,597 persons polled by telephone on Thursday and Friday, 65 percent favored a boycott, 26 percent were opposed and 9 percent were uncertain. This varies from a January survey when the margin was 73-19 in favor of a boycott.

Asked if the Games should be moved from Moscow, 74 percent approved, 18 percent were opposed and 8 percent were not sure. An earlier poll showed Americans favoring the move by an 82-13 margin.