Middle distance runner Regina Jacobs failed to enter Friday's 1,500 meters at the U.S. Olympic trials by the close of the declaration deadline Wednesday, making it likely she would become the fourth of six athletes charged with drug violations by the U.S. Anti-Doping Agency to be eliminated from contention for the U.S. Olympic team halfway through the eight-day event.

Jacobs, who tested positive last year for the designer steroid THG and recently took a job at Prudential Real Estate in Oakland, Calif., could appeal for late entry by noon Thursday with the submission of a $250 fee, but she has given race officials no indication she plans to compete.

Jacobs, a 15-time national champion, has not run this season but owned the fastest qualifying time for the event. When reached Wednesday on her cell phone, Jacobs hung up.

Quarter-miler Alvin Harrison, the reigning Olympic silver medalist in the 400, and Tim Montgomery, the world record holder in the 100, failed to qualify for the Games this week. Michelle Collins, the leading female 400 runner in the United States, withdrew because of a hamstring injury. All face lifetime bans from USADA.

The surprising spate of early eliminations has been a relief to U.S. Olympic officials who worried that most or all of the accused would win roster spots. USADA Director of Legal Affairs Travis T. Tygart said Wednesday, however, the developments would not cause the agency to drop or reduce charges against any athlete.

Before USADA took over Olympic movement testing four years ago, some athletes ended their careers when informed of drug charges to escape prosecution, but the U.S. Olympic Committee now bars such maneuvering.

"USADA does not close a drug case simply because an athlete retires or withdraws from competition," Tygart said in a phone interview. "USADA pursues all drug cases until their final resolution on the merits, not on any other basis."

Meantime, in an unexpected challenge to the authority of the four-year old agency, Rep. John Conyers Jr. (D-Mich.) on Wednesday sent a letter to U.S. Comptroller General David M. Walker requesting a General Accounting Office investigation into whether USADA has been operating outside the scope of its mandate.

In the letter, which The Post has seen, Conyers stated that "recent reports have created a cloud of uncertainty over USADA's procedures as well as the athletes implicated." Conyers raised the question of whether USADA had been "conducting selective investigations of doping violations and issuing rulings based on inadequate evidence," citing a number of newspaper stories in which charges were leveled by athletes and attorneys as to the fairness of the agency's procedures.

GAO spokesman Susan Becker said Wednesday the GAO had not had time to consider whether to take action and that the issue likely would be discussed during a weekly planning meeting Monday.

Tygart said he welcomed any inquiry into USADA's work and said the agency would speak with Conyers at any time about its operations.

"Clean athletes demand that USADA protect their right to a level playing field by eradicating drug use from sport," Tygart said. "USADA accomplishes this directive when it has sufficient evidence and not on any other basis. . . . Athletes and sports authorities around the world have applauded these efforts by the United States."

With Jacobs's apparent departure from the trials, only two of the six accused remain: Calvin Harrison, who faces a two-year ban and is scheduled to compete in Thursday's 400 final, and sprinter Chryste Gaines, who said she intends compete in the weekend's 200. Should both make the Olympic team and later be found guilty of drug violations, they would be banned from the Summer Games.

Jacobs's arbitration is scheduled to begin at 8 a.m. on Sunday, just hours before the start of the 1,500 final. Harrison's hearing is set for July 26; Gaines does not yet have a hearing date.

No events were contested Tuesday or Wednesday.

In other news, the USOC announced that the eighth-place finisher in the men's Olympic marathon trials tested positive in late January for the endurance-boosting drug erythropoietin. The athlete, Eddy Hellebuyck, is contesting the positive result in USADA's adjudication process, so no sanction has yet been imposed. Should Hellebuyck be found guilty, he would be only the second athlete banned from competition for an EPO positive by USADA.

Hellebuyck, who tried to become the oldest athlete to qualify for the U.S. Olympic track and field team at 43, won the Twin Cities Marathon last October in a master's record of 2 hours 12 minutes 47 seconds.

Notes: Lake Braddock High's Allen Johnson, seeking a place on his third Olympic team in the 110 hurdles, said Tuesday he has no plans to retire after these Games.

"This will not be my last hurrah," Johnson, 31, said. "It will not be my last Olympics -- it will probably be my second-to-last, though. There's still no one in the world that can run faster than me in the hurdles. Why quit?"