In the latest manifestation of unease among Democrats, some are quietly talking up the presidential prospects of a man who lost his party's nomination in 1988 and is about to become leader of the most discredited group of politicians in town these days: House Democrats.

He is Richard A. Gephardt, a congressman from St. Louis who was elected by his colleagues to be the House minority leader in the next Congress.While no prominent Democrat is publicly making the case for Gephardt, he is the subject of a behind-the-scenes chatter on Capitol Hill among Democrats who fear that President Clinton's popularity will not rebound and believe that Gephardt would be a logical alternative should the president decide not to seek re-election - whether by his own choice or because he is forced into early retirement.

This is the thinking of the Gephardt partisans: Having run for president, Gephardt is far better known and will get more attention than Thomas A. Daschle of South Dakota, who will be the Senate minority leader next month.

Moreover, they say, Gephardt will become only more visible as the foil to the new House speaker, Rep. Newt Gingrich, R-Ga.

And Gephardt has long been popular among working-class Democrats, a constituency that Clinton seems to have lost.

While some Democrats suggest that Vice President Al Gore would be the likely alternative should the president falter, others, like Rep. Thomas J. Manton, D-N.Y., are not so sure. "I don't know if some of the animosity toward Clinton has rubbed off on him," Manton said of Gore.

But Manton, like most of Gephardt's allies, said he fully expects Clinton to get his party's nomination in 1996.

Gephardt, who was among a handful of Democrats who considered a presidential run in 1992 when Clinton's campaign seemed to be coming apart, also dismissed the scenarios.

"All of this rumoring is just part of politics," he said in an interview Friday. "People always discuss things in terms of what exists today will exist a year and a half from now. I don't buy it. I think Clinton can win the presidency again in 1996."

But more than anyone else, Gephardt invited the speculation when he upstaged Clinton by announcing his own proposal for a middle-class tax cut just two days before the president went on national television with his own announcement.

Suddenly, he was viewed as the Democrat who is the biggest threat to Clinton, supplanting Sen. Bob Kerrey of Nebraska, an unsuccessful contender for his party's nomination in 1992.

One prominent Democrat who is advancing Gephardt's case, speaking on the condition of anonymity, put it this way: "If there's a Whitewater legal problem and an opening for the nomination, you'll probably see a Kerrey-Gore-Gephardt scenario in which I think Gephardt's a favorite. He's run before and he's got a constituency and a fund-raising base separate from the administration."