The senator is known, much as he's known outside his constituency, for a number of things: his longtime liberal leanings; his successful effort to block Nixon appointees Clement F. Haynsworth Jr. and G. Harrold Carswell to the Supreme Court; the fact that he was the Kennedy intimate who pulled the senator from a plane wreck 16 years back.

But all of this, Birch Bayh will admit, is less than the attention he's receiving as head of the special Senate subcommittee investigating Billy Carter. He made two network talk-show appearances yesterday morning; his "kisser," as he says, won on the front page of The Washington Post. He can't remember when that last occurred.

Thus it seems apt -- particularly as the senator is running for reelection back home in Indiana -- to ask what he thinks his enemies are saying about his motives for taking the spot.

The response is silence. Then -- "What enemies?" -- and a big laugh. Then, in the cadences of a Midwest farm boy, the serious reply:

"The fellow who would like to have my seat in the Senate is critical that I didn't step aside; he had expected me to step aside because Sen. Kennedy did. . . . He later had suggested, after I had been appointed head of the committee, that this whole business was not that important, though earlier he had been calling for a special prosecutor, so I think that's rather obvious. . . . My other enemies? I don't spend a lot of time thinking about my enemies. . . . I suppose they're saying all I was doing was being politically advantageous. . . ."

"Politically advantageous." That's a charge Bayh seems concerned about this week. He will not attend the Democratic National Convention, or make any comment about what he would like to see happen there because, he has decided, "it would not be prudent to express an opinion."

He will say, in a TV appearance, that he will try to move his committee quickly because "human nature being what it is, try as we will, the closer we get to November, the more temptation there will be to try to resort to politics."

Nonetheless, the question of politics for Bayh, a liberal running in a conservative state, seems inevitable.

A senator since 1962, Bayh, 52, born on a farm in Vigo County, Ind., has been seen as a candidate in the John K. Kennedy mold.

He's pro-equal rights, pro-civil rights, and he made political history in his first Senate race by defeating Sen. Homer Capehart, a nationally known Republican who had been in office for 18 years.

Since that time he has continued to be a strong liberal, so much so that he is one of the five Democrats targeted for defeat by conservative forces.

Personally anti-abortion, he nontheless backed abortion rights legislation. An early supporter of the Vietnam war, he had begun to advocate withdrawal by 1968.

He has never lost an election. He was able, in 1968, to buck the Nixon tide and defeat the then-little-known William D. Ruckelshaus. In 1974, benefitting from the Watergate backlash and police scandals in the administration of Richard G. Lugar, then mayor of Indianapolis, he won again.

In 1976 he made a bid for president, terming Jimmy Carter his greatest competitor, attacking Ronald Reagan. "I'm here because I think the only safe place for Ronald Reagan is on the late show," he said.

He was aided, in all his campaigns, by his wife, Marvella. When she was diagnosed as having cancer in 1972, he withdrew from the race. She died last year.

This fall, on his own, Bayh will face Rep. Dan Quayl (R-Ind.) in a race in which, the polls show, Bayh holds a 16 percent lead.

Still, it is a race in which his liberal reputation, his Kennedy association, could hurt.

"Birch Bayh has forgotten who he represents," says Quayle in his campaign literature. And, "If Sen. Bayh and his liberal friends remain in Washington our whole free society as we know it today is in jeopardy."

The electoral effect of his role in the Billy Carter Libya investigation, Bayh does not care to discuss. When he speaks of his role at all, he is inclined to stress the liabilities.

"There are people who want a hanging and people who want a whitewash; and the ones who don't get the hanging are gonna yell whitewash; and the ones who don't get the whitewash are gonna yell hanging."

And the assets of being in the limelight during an election year?

Bayh shrugs them off.

"A very short-termined benefit," he says. "Like walking in a mine field."