A mellow black tenor from Washington played a tough white audience in the heart of ethnic Milwaukee last night and brought down the house.

D.C. Delegate Walter Fauntroy came to Serb Hall, a neighborhood gathering place that not so long ago was the home of Milwaukee's antibusing activists, for a campaign rally with presidential candidate Edward M. Kennedy. After a shaky start, Fauntroy got a huge ovation with a stirring rendition of the song that has been his political trademark -- "The Impossible Dream."

Fauntroy has been campaigning around the country for Kennedy for months, mostly before black crowds, and that song has been a standard part of his repertoire. He will start singing a capella without warning in mid-speech, and audiences generally have reacted with gasps of surprise.

But the first surprise here was that Fauntroy showed up at all at Serb Hall, a traditional meeting place for the Serbian, German and Polish families in the city's working class neighborhoods. In years past, the hall was the scene of some of the most successful rallies of George Wallace's presidential campaigns, and tub-thumping neighborhood protests against school busing.

"This may be a first," said Patrick Lucey, the former Wisconsin governor who is running Kennedy's campaign here. "I've never heard of a black politician going to Serb Hall before."

The D.C. delegate was at a disadvantage from the start because he did not speak until after three local politicians had had their say and Kennedy had delivered a rip-snorting stump speech. When Fauntroy got up and began explaining in his high, thin speaking voice about the Congressional Black Caucus, people started leaving in droves.

But the exodus stopped when Fauntroy quoted Martin Luther King Jr., then pointed to Kennedy and said, "This man, too, dares to dream the impossible. . . ." And then he was off into a soaring, highly dramatized performance of his song.

With inflection and theatrics, Fauntroy managed to suggest that the lyrics of the old standard were actually about Kennedy and his quest for the presidency.

"The world will be better for this," Fauntroy said, walking towards Kennedy. "That one man, scorned and covered with scars" (here he put his arm on Kennedy's shoulder) "still tried, with his last ounce of courage . . . to fight the unbeatable foe." (Here he held up a newspaper with Jimmy Carter's picture.)

"To give" Fauntroy sang, holding the note for a long half-minute as he pulled out a $20 bill and gave it to Kennedy with a flourish, "when there's no more to give" -- and he held the note again, displaying an empty wallet to the laughs and cheers of the crowd.

By the time Fauntroy belted out the song's last line ("to reach the unreachable staaaar") the sheer astonishment of the faces of the Serb Hall crowd had changed to smiles of delight and admiration, and the singer got a whooping, shouting round of applause.

But nobody liked the show better than Kennedy, who roared out a cheer when Fauntroy finished. Then at a joint Kennedy-Fauntroy press conference here this afternoon, Fauntroy launched into a heavy speech about Kennedy's commitment to minorities, and Kennedy stood in the background singing, "To dream the impossible. . . ." The press corps joined in an everybody serenaded Fauntroy with his own song.

It was Kennedy's own idea to bring Fauntroy to Serb Hall. The candidate had been bowled over when Fauntroy put on a similar performance, complete with the passing of the $20 bill, in Montgomery, Ala., a month ago, and when he heard that Fauntroy was in Milwaukee campaigning for him, he insisted that the delegate attend Sunday's rally.

After Fauntroy's earlier performance in Montgomery, by the way, Fauntroy and Kennedy fled back together to Washington. At National Airport, Fauntroy turned to Kennedy and asked for his $20 back so he could take a cab home.