America's Cup challenger semifinals hit the midway point today with four of the six contenders still firmly in the running to advance to two-boat finals and a controversy swirling around Dennis Conner's Stars & Stripes.

AmericaOne (4-1) and Prada (3-2) continued their recent winning ways with easy victories over strong rivals in light winds. They lead the series with five races to go.

AmericaOne scored a lopsided win over Stars & Stripes (3-1), which had shocked the fleet by winning its first three semifinal races after finishing fifth in the early rounds. In addition to absorbing its first loss, Stars & Stripes was accused by rival Nippon of using an illegal rudder in their opening-day race, a charge that if upheld could cost Stars & Stripes that earlier win--and more.

"The context in Article 19 of the protocol is loud and clear," the Japanese said. "You are only allowed to manufacture appendages in your own country [that is the United States in Dennis Conner's case] or in New Zealand."

At issue is Stars & Stripes' one-time use of a new rudder made in Australia. Conner's team removed the new rudder and replaced it with an old one after beating Nippon on opening day of the semifinals, when it became clear its legality would be questioned.

On Friday night, an international jury found that the rudder was made in Australia, then sent its findings to an arbitration panel to determine if that indeed violated the rules.

Jury chief Brian Willis would not speculate on what penalties might be assessed if Stars & Stripes is found in the wrong, but knowledgeable observers suggested Conner's team could at least be stripped of its win over Nippon and at worst might be tossed from the regatta.

Stars & Stripes tactician Tom Whidden expressed "total surprise" at the challenge. The team maintained in a written submission it had done nothing wrong. No ruling was expected before Saturday night.

Meantime, standings at the top two-thirds of the six-boat fleet remained tight.

Conner called the fleet "the most professional I have ever seen," with no weak players. In Friday's racing, Nippon gave AmericaOne all it could handle before losing by 23 seconds, and winless Le Defi Francais pushed regatta favorite Prada to the limit before falling behind on the next-to-last leg to lose by 18 seconds.

That close racing gave way to more one-sided competition today as the wind went light and shifty, which usually separates the boats. Racing was delayed for more than an hour as organizers waited for the sea breeze to fill.

The first pair off the line in 7 knots of wind was Prada and Nippon. Nippon's aggressive skipper, Peter Gilmour, convincingly won the start. But Prada, the silver Italian speedster that had lost only three times in two months of preliminary racing, easily passed the Japanese on the first upwind leg, profiting from better winds on the right side of the course.

Prada struggled in the early going of the semifinals, losing one race to Stars & Stripes because of poor crew work and another to AmericaOne when its mast snapped in half. But Prada showed no weakness today, extending its lead over the swift white Japanese sloop with flawless tactics and superior boat speed to win by 1 minute 33 seconds.

AmericaOne's Paul Cayard, seeing the advantage on the right side of the course that Prada enjoyed, battled and won the right side of the starting line 10 minutes later against Stars & Stripes. Cayard tacked to follow Prada's route and almost immediately shot out to a one-minute lead.

AmericaOne never was challenged as Stars & Stripes showed its suspected weakness in light winds and lost by 2:43.

In the third race, the closest of the day, Le Defi Francais, winless to date, finally got on the scoreboard, using excellent light-air speed to dispatch San Francisco's America True by 36 seconds.

Only America True (1-3) and Le Defi (1-4), appear out of the running for a berth in the two-boat challenger finals that start Jan. 25. But both have shown the speed to beat any of the higher rated boats in certain conditions and could prove spoilers.

"Everybody has stepped it up," said Terry Hutchinson of Annapolis, mainsail trimmer on AmericaOne.

And with five days of racing to go, all the top teams are feeling the pressure as their multimillion-dollar, multiyear quests wind down to a few opportunities.

The Standings

Semifinals in Auckland,

New Zealand

Team W L Pts

AmericaOne 4 1 4

Stars & Stripes 3 1 3

Prada 3 2 3

Nippon 2 3 2

America True 1 3 1

Le Defi Francais 1 4 -.5

(Each team sails against the others twice. Victories are worth one point each. The top two boats will advance to the best-of-nine finals to decide who takes on defender Team New Zealand in February. Le Defi Francais was penalized half a point for a collision.)

Friday's results

AmericaOne def. Nippon by 23 seconds.

Prada def. Le Defi Francais by 18 seconds.

Saturday's races

Prada def. Nippon by 1 minute 33 seconds.

AmericaOne def. Stars & Stripes by 2 minutes 43 seconds.

Le Defi Francais def. America True by 36 seconds.