United States and Canadian amateur bike racers Davis Phinney and Steve Bauer astounded some of Europe's strongest professionals today, leading an early breakaway in the 62.5-mile, $100,000 U.S. Professional Cycling Championship around Baltimore's Inner Harbor.

The underdog victory by the two North American amateurs in the richest and most widely televised one-day bicycle race in U.S. history compared to the hometown middle-class "cutters" beating elite college teams in the popular bicycling film "Breaking Away."

The American-Canadian triumph brought cheers from a crowd of more than 80,000, many swarming across police lines and disrupting the end of the race.

The 2 hour 28 minute Inner Harbor Race--eight minutes faster and with $75,000 more in prizes than last year's first U.S. Pro in Baltimore--was hailed by race officials as a great day for bike racing in America.

Five of the first nine riders to finish were amateurs, three of them Canadians. And Phinney's fellow U.S. Olympic team member, Wayne Stetina, came in seventh while Stetina's brother Dale, now a pro, finished 16th, just behind John Eustice, who retained his title as U.S. professional champion. Eustice's 15th was the best placing by a U.S. pro.

Eustice was the first American in last year's U.S. Pro here when he was sixth, but his showing today was a pleasant surprise for a man who incurred severe facial injuries in a bike accident three months ago.

Phinney and Bauer, the two 23-year-olds who only last week won the U.S. Amateur National Championship in Somerville, N.J.--but in reverse order, with Canada's Bauer edging Phinney by two inches--broke away from the field on the fifth lap of the 42-lap race, along with Ferdi Vandenhautte (Belgium) and Alan Peiper (Australia), two professionals who ended third and fourth, respectively.

Apparently the amateurs and the two lightly regarded professionals were not considered a threat by the international field of 79 riders from 15 nations. No sustained effort was made immediately to catch the breakaway group.

"I hoped to break away early because of the heat," Phinney said. "I think the heat (85 degrees) really hurt the pros," most of whom flew in Friday from a cold, wet spring of European racing.

"But I also think the pros underestimated the amateurs . . . and the crowds were for us. I was racing for America and I felt terrific because of the crowds and knowing so many people were watching on TV," Phinney said.

Bauer and Phinney, who have turned down offers to join professional teams--they ride for U.S. and Canadian Olympic teams but are sponsored by 7-Eleven and G.S. Mengoni, respectively--will get only $950 each of the $25,000 and $15,000 first and second prizes. The rest of the money will go to amateur cycling federations in the two countries.