The senior U.S. member of the International Olympic Committee (IOC) said yesterday that he thinks the IOC would cancel the 1980 Summer Olympics in Moscow if the United States and a substantial number of other countries decided not to participate because of the Soviet invasion of Afghanistan.

Douglas F. Roby of Ypsilanti, Mich., one of two Americans on the 89-member IOC, predicted that a U.S. proposal that the Moscow Games be relocated, postponed or canceled would be "turned down flat" when the IOC meets next week at Lake Placid, N.Y. But subsequent decisions by a number of Western and Third World countries not to send athletes to Moscow could lead to cancellation of the Games, he said.

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Asked what he thought the IOC would do if the national Olympic committees of the U.S. and three dozen or more other countries declined invitations to the Games at the request of their governments, as the State Department has forcast, Roby said:

"I think if that happened, it would be cancellation. In other words, if it got around to that point, the IOC would say, 'We will not celebrate the Games of the 22nd Olympaid.' I certainly don't think they'd hold a set of Games that weren't a credit to the Olympic movement."

Roby said that moving the Games to another site or several sites on short notice would be "out of the question, in my opinion," because of the result would be "a half-baked set of Games, and we don't want that."

Other IOC officials have said that cancellation is the only alternative to holding the Games in Moscow as scheduled, July 10-Aug 3, but would be considered only in the case of "a force majeure, such as a natural disaster or world war." The Olympcis of 1916, 1940 and 1944 were canceled because of the world wars.

Roby is part of the U.S. Olympic Committee (USOC) delegation that is scheduled to meet privately with IOC President Lord Killanin and the IOC's Executive Committee on Friday and Saturday to discuss the future of the Moscow Games.

Roby and Julian K. Roosevelt of New York are the two American members of the IOC who will vote on the USOC proposals when it comes before the full IOC next week.

In a telephone call to The Washington Post, Roby criticized President Carter for a speech last week which he said amounted to "waving a red flag in front of the IOC."

Roby said the president's pledge to help organize "international games of the highest quality" outside the Soviet Union this year if Soviet troops are not fully withdrawn from Afghanistan by Feb. 20 had angered members of the IOC and guaranteed unfavorable reception for the U.S. proposal at the IOC session next Sunday, Monday and Tuesday.

"It's all right for the president to recommend that Americans not got to Moscow, but his suggestion of setting up other Games, that would be impossible," said Roby, a past president of the USOC and an IOC member since 1952.

The official IOC position has been that no nation is obliged to enter the Games, and can decline to participate without penalty up to the May 24 deadline for accepting invitations.

However, according to the IOC Charter, decisions must be made by national Olympic committees free of government interference.Moreover, any effort to organize alternative games is regarded by the IOC as a threat to the Olympics, which it owns.

The executive board of the USOC voted last month, at President Carter's request, to petition the IOC to transfer this summer's Games from Moscow to another site or sites, postpone or cancel them. It deferred until after the IOC meetings any action on the president's further request that the U.S. not send athletes to Moscow if the Games go on there and Soviet troops are not fully withdrawn from Afghanistan.

In a speech last Friday, the president praised the USOC's "courageous action" and said that the U.S. and like-minded nations must make it clear to the Soviet Union that it cannot engage in aggression and "expect to conduct business or sports as usual with the rest of the world."

He also said that he was "determined personally" that athletes from all around the world "will have an opportunity to participate this year in international games of the highest quality," but not in the Soviet Union if Soviet troops remain in Afghanistan.

This part of the speech, reinforced by statements from White House and State Department aides that the Carter administration would support financially and logistically the organization of alternative games, apparently distressed many IOC members.

"I don't know why he had to inject this sort of thing at this time, with the IOC meeting as a body within a week. There's going to be some real fireworks as a result of this," Roby said, insisting what Carter's speech had doomed what slim chance the USOC proposal might have had of gaining favorable response from the IOC next week.

West German Chancellor Helmut Schmidt arrived in Paris yesterday for meetings and French President Valery Giscard d'Estaing, and the issue of the Moscow Olympics was expected to be high on the agenda of their discussions.

The German and French Olympic committee have said they will decide on the participation of their athletes without interference from their governments, but it is doubtful they would act contrary to a direct government order.

West Germany and France are considered pivotal nations is achieving any mass pullout from the Moscow Games.

The governments of 18 countries -- including Japan, China, Canada, Australia, Great Britain and New Zealand -- have said that they oppose participation of their athletes in Moscow, and their national Olympic committees are expected to go along.

The State Department said last week that at least 17 other governments privately have expressed support of a pullout, and the number is expected to rise.

Meanwhile, public support for American withdrawal from the Moscow which has been reflected in the overwhelming approval of resolutions to that effect in both houses of Congress -- has increased dramatically in the past two weeks, according to a new Associated Press-NBC News poll.