If Carter sinks, could Muskie swim?

A small boomlet is emerging for Secretary of State Edmund S. Muskie to replace President Carter on the fall Democratic ticket. Mr. Muskie himself acknowledges that a push along this line is developing. "I hear these reports," he told a group of reporters over breakfast on July 22.

Asked whom he is hearing this from, Muskie answered: "I hear from average citizens."

Then he gave what might be called the "expected" response -- that he "would discourage" those who would try to bring this about. And he added with a smile, "I would rather be secretary of state than be president."

But what Muskie was acknowledging is that as Mr. Carter sinks lower and lower in the polls, he has, indeed, become the central figure in a movie within the Democratic Party -- mainly from Kennedy-oriented liberals -- to try to depose Mr. Carter and put in the former Maine senator and governor as substitute.

"Playing the Muskie card" has been the subject of some speculation for some weeks now. Along with Vice-President Walter F. Mondale, he is discussed as a possible compromise alternative to President Carter if Sen. Edward M. Kennedy is unable to turn the convention in his direction.

And in recent days the Muskie possibility has been gaining ground as key politicians have passed along this view:

They feel Mr. Mondale's close tie with the President and, particularly, Mondale's criticism of Senator Kennedy during the primaries, would make the Vice-President much less acceptable to Kennedy delegates than Muskie.

The President retains, meanwhile, a strong hold on the convention as the result of his primary victories and is likely to keep it from moving away from his own nomination.

But leaders in the Kennedy camp say they are convinced that if at convention time the President looks like a sure loser, Carter delegates could be persuaded to leave their candidate and accept a possible winner -- someone like Muskie, who draws support from Democrats all across the ideological spectrum.