The lead in the 284-mile, three-day Tour of America bike race changed dramatically late this afternoon in a rainy 9.3-mile time trial in Richmond National Battlefield Park.

Dutch sprinter Bert Oosterbosch, who got off the plane from Paris on Thursday predicting he would win the time trial and probably the Tour of America, took the lead in the $100,000 race with a fierce pace that left even the closest of the 74 other racers 33 seconds behind.

Australian John Anderson was second-fastest in the time trial, putting him in second place overall going into Sunday's final day of racing. Danish rider Dag Erik Pedersen was third, French sprinter Jean-Marie Grezet fourth and Canadian amateur rider Steve Bauer fifth.

Earlier today, about 15,000 rain-drenched Richmond residents cheered Oosterbosch's teammate on the T.I.-Raleigh Team, Leo Van Vliet, and French rider Pierre Le Bigaut as they scored the first successful breakaway of the race to win the 83-mile ride in the rain from Williamsburg. The race ended on slippery, hilly Richmond streets, where cyclists struggled up cobblestones and dashed down hills at more than 50 miles an hour.

But in accepting the race leader's yellow jersey at 1:30 p.m. in front of the state capitol, Van Vliet, shivering and covered with mud, predicted he wouldn't wear it long and that Oosterbosch would shortly win it from him.

Sunday's race is expected to attract even larger crowds, especially if the rainy weather ends by the time riders reach Washington about 2:45 to 3 p.m. The race will end with six laps around the Tidal Basin and Mall, similar to the five-lap final today around downtown Richmond. But it should be faster as there are no hills, railroad tracks and wet cobblestones to cross.

On Friday, on the first 114-mile stage from Virginia Beach to Williamsburg, the riders finished in a tight bunch after attempted breakaways were caught by the pack. All riders were given the same time, except for the first three, only inches ahead of the pack, who won six-, four-, and two-second time bonuses. These few seconds, plus small time bonuses awarded for two sprints during each day of racing, put the first and last cyclists in the race only seconds apart.

After today's racing, 15 minutes separated the first and last riders.

Today's race started in the simulated French village in Busch Gardens outside Williamsburg, but stopped briefly before the red flag was waved for an "arret pipi," in which most of the racers and officials in close to 100 cars and motorcycles leaped from their vehicles to stand beside the road. The scene, like most of the racers in the tour, was very French.

The last racer to arrive up the slippery cobblestone street by the capitol, part of a six-mile circuit in downtown Richmond that riders sped around five times, was Paul Pearson of Bethesda, Md., known as "the Animal" for his unrestrained riding. Pearson, on the U.S. Pro Team, was one of the few racers to make a long breakaway during today's race, a solo effort that eventually failed and left him exhausted.

French and American race promoters were unhappy with the rain--as were the cold, mud-covered riders--but they were delighted with the crowds and the second almost accident-free day of the race.

John Herety, the British national sprint champion, took the race's only fall so far on a slippery corner, but was not seriously injured. He finished 25th in today's leg.

Probably close to 50,000 spectators lined the route to Richmond to cheer, wave flags and show signs saying, "Allez Belgique," Vive la France" or "Vive la Italie."

Many were unwitting spectators, because police and hundreds of volunteer marshals stopped traffic along all side roads while the race entourage passed.

John Patterson, on the same U.S. Pro Team as Pearson and Jonathan Boyer, was the top-ranked American after today's race, in 10th place. Patterson won time bonus points for breaking away and finishing second on one of two sprints up Richmond's hills.

Many riders on the tour continued to complain of jet lag from having flown from Paris only 16 hours before the start of the race, including Boyer and Peugeot team captain Anderson, who led the 1982 Tour de France for much of the 22-day race last summer.

Most of the racers are from Europe, the majority from France. Others come from Holland, Belgium, Australia, Norway, Canada and England.

The racers are enjoying their visit despite the wet weather. Herety, on his first trip to the United States, said, "Everybody's very friendly, even though most people along the road don't know what's going on."