Vice President Mondale said today that the 1980 summer Olympics should be moved out of the Soviet Union because a Moscow Olympiad would grant "legitimacy" to a country that has "committed an outrageous and indecent act of aggression."

Mondale said that moving the Olympics was his personal idea, but that he had urged it upon President Carter and the question was under study in the administration.

And Mondale, campaigning here as a stand-in for the president, said that Carter challenger Edward M. Kennedy was motivated by "the politics of the moment" in criticizing the administration's embargo of some grain sales to Russia.

Mondale said that in considering the best reaction to the Soviet invasion of Afghanistan, Kennedy, like Carter, had to decide "whether to do the political thing or the thing that best serves this nation."

Kennedy, he said, chose politics. But Mondale said Carter rejected political considerations in deciding to limit grain sales.

"The president knew that the easiest thing to do politically was to duck this one," Mondale said. But Carter "put the country first."

Mondale said that representatives of major farm organizations and many Iowa farmers have announced their support of the president's decision.

Kennedy, on his return to Iowa later today after campaigning in Illinois, siad: "I don't think I or the members of my family need a lecture from Mr. Mondale or anyone else on patriotism.

"I have too high a regard for Vice President Mondale to question his decency or loyalty or his patriotism, and nothing that happens during the course of this campaign will alter the high regard I have for the vice president," he said.

Kennedy said that both he and Mondale were among senators who dissented from continued U.S. involvement in the war in Vietnam and were accused at the time of being unpatriotic.

The vice president talked about the Olympics repeatedly on this first day of a three-day tour intended to galvanize Carter supporters for the Jan. 21 Iowa precinct caucuses.

Mondale's visit will end in Waterloo Saturday night where he, Kennedy, and California Gov. Edmund G. (Jerry) Brown Jr. are all scheduled to address a party dinner.

En route to Iowa this morning, Mondale told reporters on Air Force Two that he was greatly impressed by a column on the Op-Ed page of today's Washington Post that said loss of the Olympics would be a severe blow to the Soviet leadership's quest for legitimacy. He said he phoned the president right away to urge that he read the column.

As soon as he landed in Des Moines, Mondale brought up the subject again. "It is my personal belief that the Olympics ought to be held somewhere else, somewhere where they have facilities" he said, mentioning Montreal and Munich as possible sites.

"This would permit athletes from around the world to hold that important event without politics but not in a setting where we are in effect granting legitimacy to a country that has just committed an outrageous and indecent act of aggression."

In his speech last Friday announcing the U.S. response to the Soviet invasion, Carter raised the possibility that U.S. athletes might stay out of the Moscow Olympiad.

Mondale's longest stop in Iowa today was in the small dining room of Maurice Furlong's farmhouse just south of this Mississippi River town.

Grandma Moses paintings hung on one wall, and on the other were graduation photos of all seven Furlong children. Furlong and eight other local men sat around the table with the vice president while their wives waited in the living room.

The nine farmers politely asked about the need for the grain embargo and its impact on Russia and on the United States. Mondale answered in a friendly, easy way, telling them that after "a few rough days" grain markets would settle down and the impact on farmers would be minimized.

The farmers asked some specific questions, but received mainly generalized answers.

When one man asked how soon the administration could set up the massive gasohol production program it has promised to absorb excess grain, Mondale talked about government loans and tax credits and cracked a joke about bootleg whiskey, but did not answer the question.

Afterward the men and women said they were genuinely impressed that Mondale had taken the time to talk to them, but they said they were still worried about the impact of the embargo on the price of their products.

Tom Furlong, the host's 30-year-old son, said he had been an active Carter supporter "before" -- that is, before the grain embargo. Now, he said, he is likely to stand as "uncommitted" at his precinct caucus 11 days from now.