The Irish national team, Olympic medalists and many top U.S. amateur and professional cyclists -- including Davis Phinney and Rebecca Twigg -- will ride today in the 18th annual National Capital Open bicycle races on the Ellipse.

With more than 500 cyclists entered, it will be the largest and also one of the nation's most diverse bike racing fields -- with nine races, two for women and seven for racers from ages 9 through 40, starting at 8:30 a.m.

The featured women's and men's races, which start at 1 and 2 p.m., respectively, will have the most competitive packs of riders ever to spin their wheels on the fast, flat oval behind the White House.

The field became more competitive in recent weeks with the late influx of top riders such as Phinney, whose 7-Eleven team left the European racing circuit and the Tour of Spain after the outbreak of terrorist acts and threats against Americans. Racers can enter most bike races until moments before the starting gun.

Phinney and Olympic silver medalist Twigg both won the week-long Beatrice Bicycle Classic in Texas last month, the most prestigious American stage race after the Coors. Twigg won the Open the last time she raced here in 1982. Both are considered among the world's best criterium cyclists -- in races of 30 to 75 miles on short loop courses like the Ellipse's. Criteriums are the most popular U.S. bike races, though less common in Europe, because crowds have an almost constant view of the racers.

Also favored in the featured men's "pro/senior I and II" race are Leonard (Harvey) Nitz, the sprinter who has won 13 national championships and won the Open in 1985 and 1979; Germany's Olympic double-medal winner Gregor Braun, and criterium specialist Alan McCormack of the Irish national team. Also registered is three-time Open winner Bruce Donaghy of the Alfa-Romeo bike team -- who beat Nitz here in a close finish in 1981.

In the women's "A" race other favored riders include Twigg's 7-Eleven teammates, Inga Thompson and Connie Paraskevin, who holds three world sprint titles and is nine-time U.S. national track champion; and Carol Addy, a strong criterium rider for the Fuji-Suntour team featured in Fuji-Suntour ads.

Four-time Open winner Betsy Davis, of Bogota, N.J., who won the recent Texas Cup criterium and who won here last year, is considered likely to race, according to Bill Wilkinson of the Bicycle Federation of America, which is jointly promoting and organizing this year's Open with the National Capital Velo Club. The Embassy of France and Mel Pinto Imports founded the race and remain its official sponsors.

The Washington-Baltimore region will provide most of the favorites for the barely-over-the-hill veterans class race (ages 35-40), with national and former NCO champions Jim Montgomery, Bobby Phillips, Rob Lea and Jerry Nugent.

The Open this year offers $11,000 in prizes, mostly in merchandise, plus bonuses for winning laps or "primes." The race is now also part of the 7-Eleven Cup Series, a grand-prix style series of 26 U.S. races with riders earning points toward $80,000 in prizes.