In a dramatic fall from political prominence, Maryland's Rep. Robert Bauman was soundly defeated in his reelection bid last night, deserted by thousands of former supporters after revelations of his troubled sex life.

The Easton Republican, once a rising star of the Republican right, appeared at 1 a.m. to concede defeat to Democrat Roy Dyson before a small group of subdued supporters and a mob of reporters at the elegant Tidwater Inn in his hometown.

"We are at peace with ourselves and with God and that's what's most important," said Bauman, echoing the tones in which he asked for forgiveness and "one more chance" in the final, feverish weeks of the campaign. "I have come through this campaign with a far deeper understanding of the suffering of those who are troubled and those who are less fortunate."

Bauman's 15-year-old daughter, Genie, clutched him around the waist as he stood on a mahogany chair to address the crowd, and he, in turn, held her close to him.

In a confident parting aside to the press, the Bauman known for his sarcasm and conservative sharp-shooting in Congress, smiled and said: "Who knows?You may have me to kick around again sometime."

Meanwhile, at the other end of the district, Dyson, the congressman-elect who was considered a sure loser until Bauman's troubles were made public, stood before supporters at a Holiday Inn in Aberdeen and promised with tears in his eyes: "You're going to see a very active congressman."

With more than 90 percent of precincts reporting, Dyson had a 4 percent lead over the three-term incumbent.

A southern Maryland state delegate and moderate Democrat, Dyson was transformed from anonymous underdog to frontrunner on Oct. 3, when Bauman was charged in a Washington courtroom with soliciting sex from a 16-year-old boy.

Bauman, who had easily defeated Dyson four years ago, saw his political base erode as returns rolled in from throughout the sprawling district. He lost three of the seven counties on his home turf, the Eastern Shore, which he swept in 1976. Dyson cemented his lead with victories in southern Maryland and the northern counties of the district, and a strong showing in Harford County, home of one-quarter of the electorate.

At Bauman's election-night gathering, supporters bitterly blamed the press and "political mudslingers" for their candidate's defeat, saying the campaign was focussed on Bauman's personal life rather than on his voting record, one of the most conservative in Congress.

"It's a sin, it's a travesty," fumed Randi Jones, a Democrat who worked for Bauman in Snow Hill. "That man is nowhere near Bob Bauman. I hope that Roy Dyson stays as lily white as any man can be in the next two years, or the 1st District is going to crucify him."

Dyson repeatedly refused to discuss Bauman's troubles and when he appeared at 1 a.m. to claim victory, he called the campaign "honest and honorable."

His campaign manager, Tony Pappas, however, acknowledged the impact of the sudden disclosures. "Certainly it had an effect," he said. "The people of the First District are a very moral and conservative people and so is Roy Dyson."

In the last weeks of his campaign, Bauman worked hard to try to offset the devastating political impact of his Oct. 3 court appearance, when he pleaded innocent and entered a court-supervised rehabilitation program.

But the revelations continued.There were widespread reports that he had frequented Washington's gay bars for months. A man identified by police as Bauman's ex-lover was charged with attempted extortion after threatening to reveal their affair unless Bauman paid him hush money.

What made things even worse for Bauman was his position as a champion of ultraconservative causes, a favorite of such organizations as Moral Majority and a legislator who showed no sympathy for the personal weaknesses of his adversaries.

But after five days of seclusion following his court appearance, Bauman, 43, burst back onto the campaign trail with an emotional press conference in which he admitted having "twin compulsions" of homosexual tendencies and alcoholism and vowed to fight for reelection. With his wife, Carol, constantly at his side, he openly asked for forgiveness, admitting, "I have done wrong," but also telling voters to judge him on his record, not his personal life.

By contrast, the 31-year-old Dyson scrupulously avoided any mention of Bauman's personal problems except to express "sympathy for his plight" while stumping the state in workmen's boots that, by the end of the campaign, had a hole in one sole.