A White House aide left open yesterday the possibility that the Carter administration might approve the participation of Americans in the 1980 Summer Olympics in Moscow if Soviet invasion forces are removed from Afghanistan between the Feb. 20 deadline set by the president Sunday and the late spring and early summer dates for filing Olympic entries.

In the unlikely event that there were a "real, legitimate withdrawal" of Soviet troops after Feb. 20 but before the early July deadlines for submitting names of Olympic team members to the International Olympic Committee (IOC), American athletes might receive their government's approval to compete in the Moscow Games, the aide told The Washington Post.

The administration thinks there is "a very slim chance" of any significant withdrawal of Soviet troops in response to the president's request not to send athletes to Moscow, and will continue to concentrate its Olympic efforts on trying to get the Games shifted to an alternative site, postponed or canceled, the aide said.

The president said Sunday in a television appearance on NBC's "Meet the Press" that "neither I nor the American people would support the sending of an American team to Moscow with Soviet invasion forces in Afghanistan," and requested in a firm, 750-word letter to Robert J. Kane, president of the United States Olympic Committee (USOC), that Americans not go to Moscow unless Soviet troops were fully withdrawn within four weeks. n

However, officials of the USOC, who still hope to salvage American participation in this summer's Games, see the early July deadlines for submitting the names of Olympic team members as the point of no return for a decision on going to Moscow. The deadlines for naming teams in the 21 Olympic sports all fall between July 1 and 10.

An earlier cutoff could be May 24, eight weeks before the scheduled start of the Moscow Games on July 19, when each country's Olympic committee must inform the IOC of the sports in which it intends to enter teams.

The USOC, whose executive board will meet in Colorado Springs this weekend and consider the president's request, would like to delay a final decision as long as possible and is currently going ahead with plans to conduct Olympic trials in 17 sports between March and July.

"Now we have a month's flexibility. We have a chance to talk to other nations, to see whether possibly world tensions will be relaxed, and to hope for a miracle -- that the Soviets will move out of Afghanistan," said Kane, who thinks it is "infeasible" to relocate the Games this year and unlikely that the IOC can be persuaded to postpone them.

Asked what would happen if the Soviet Union did not withdraw its troops from Afghanistan by Feb. 20, but did so before the Olympic entry deadlines passed, the White House aide said: "That's a good question. We really haven't focused on that yet, but we will.

"It would depend on the circumstances under which the Soviets left. If they technically withdrew, creating an Afghan puppet and leaving troops at the border, that would be one thing. If there were a real, legitimate withdrawal, that might be another.

"Withdrawal in a month, as the president stipulated, would mean a real withdrawal because there's nothing the Soviets can do to subjugate the Afghan people in a month. If it's in four months, it depends a lot on what they have done," he said.

The aide indicated that the one-month deadline was decided arbitrarily, but with careful consideration.

"The president had to give the Soviets some time to comply and withdraw their troops, but couldn't give them much more than a month or there would be no chance of finding an alternate site for the Games," he said. "There's little enough time as it is."

Since the administration sees little chance of an early withdrawal by the Soviets, the White House is directing most of its Olympic efforts toward having the Games moved to another site, and enlisting the support of allies and Third World nations for a position similar to the president's -- that the Games should be boycotted if they are not moved from Moscow.

The IOC has remained adamant in its position that the Moscow Games cannot be postponed, canceled or moved. Lord Killanin, IOC president, has issued statements to this effect almost daily in recent weeks.

"We do not accept the Killanin position that it is technically and legally impossible to move the Games," said the White House aide. "if the nations of the world really want to do it, it could be done.It wouldn't be easy, but it could be done."

Montreal and Los Angeles are now considered the most viable alternative cities by the administration, because both could use college dormitories in lieu of an Olympic Village. White House aides have advanced the possibility of housing athletes on campuses an hour or two from the site of the Games, where they would have first-class athletic facilities for training, and flying or busing them in for competitions.

Meanwhile, it was learned that the USOC had decided to delay polling the about 10,000 athletes who will be invited to Olympic trials in the various sports as contenders of the U.S. team until after Feb. 20.

Kane and USOC Executive Director F. Don Miller issued a statement after a White House meeting last Friday with Secretary of State Cyrus R. Vance and other administration officials saying that "if the president of the United States advocates a boycott, we will immediately poll prospective members of the U.S. team to ascertain their feelings about such an action. Based on the collective view of the athletes, the USOC Executive Board will then make a decision on whether or not to enter athletes in the Games."

The USOC has chosen to interpret President Carter's position not as advocating a boycott, but merely as announcing his intention to do so if Soviet troops are not out of Afghanistan within a month.

Using this rationale, they have given themselves more time to devise a procedure for polling the athletes, a more difficult task than it seems at first glance because the USOC does not have any comprehensive list of potential Olympians in every sport and no easy means of identifying and contacting them.

Apparently, the poll will be conducted by the National Governingng Bodies (NGBs) of each sport, which fall under the umbrella of the USOC organization. The athletes technically do not come under the jurisdiction of the USOC until they have earned places on the Olympic team because it is the NGBs that conduct the Olympic trials, with USOC approval.

At least one of the 86 voting members of the USOC Executive Board, meanwhile, said that a proposal to support the president's position would likely be tabled at next weekend's meeting until the matter could be studied further and the athletes polled.

A White House representative, probably presidential counsel Lloyd Cutler, will attend the meeting and probably will urge the USOC panel to vote not to send a team to Moscow unless Soviet troops are withdrawn.

The administration yesterday down-played the prospect of having to seek or to use legal sanctions to prohibit Americans from going to Moscow if the USOC votes to send a team, insisting "that won't be necessary, and in no way did we wish to imply that we would do it."

Cutler raised the possibility in a briefing Sunday, saying, "I feel sure the U.S. government, if necessary and if it decided to do so, could prevent U.S. athletes from participating in the Games."

White House spokesman Jody Powell immediately added, "We do not anticipate that that would be necessary. That is a bridge that we have not crossed, and we do not think it will be necessary to cross."

Administration officials emphasized yesterday that they are confident that the USOC and American athletes, cognizant of widespread public support for the president's position, will voluntarily abide by it.