Rosie Ruiz promised today she will prove to the nation that she is a world-class runner, but not until July.

The unknown and -- for many of the Boston marathon competitors -- invisible woman who took home the gold medal as the fastest female called a press conference today to rebut accusations that, if true, would make her the running world's No. 1 fraud.

At her side, as her chief adviser and defender against an outraged running establishment, Ruiz had Steve Marek, who stands accused of cheating in a New York marathon that he entered wearing a Superman suit.

By turns tearful, defensive and defiant, Ruiz handled a long series of questions before being asked what she would do if the Boston authorities -- as is reported likely to happen soon -- strip her of her medal for not having run the whole race.

A Boston television station, WBZ-TV, reported that officials of the Boston Athletic Association, which sponsors the annual Patriots Day race have completed their investigation into allegations Ruiz did not run the entire 26.2-mile course. The station reported Ruiz will be disqualified Friday and Canadian Jacqueline Gareau named the official woman's winner.

"If they take my title away," Ruiz began. The she bowed her head over the marathon medal hanging around her neck and wept quitely into the nest of microphones clipped to the lectern.

Kay Williams, one of Ruiz's room-mates, said "It's been like everyone's hyper." They have moved out of their high-rise apartment near Times Square to get away from reporters and other curious people, some of whom have been sneaking past the building's security guards, Williams said.

Ruiz moved in with Williams and another woman in the fall of 1978 after undergoing the second of two brain operations. The first operation removed a tumor that was found to be benign, and the second one, in September, installed a plastic plate in her skull. Only in February of 1979 did Ruiz begin to feel well enough to run, Williams said.

Ruiz's first race was in New York Marathon last October, and Williams says she remembers going to the eight-mile mark to wait in case Ruiz wanted to drop out at that point.

"I think I'm going to finish," Ruiz reportedly said as she ran by. "I feel good."

Officially, Ruiz finished 24th among the women in 2:56.29. That clocking qualified her for the Boston marathon.

The Boston result prompted Fred Lebow, organizer of the New York Marathon, to check videotapes made at the finish line. Ruiz wasn't there when her clocking said she should have been and she wasn't among the 100 finishers ahead or behind her time, Lebow said.

Ruiz is vague about how she trains, where she trains and why she has escaped the notice of the dozens of running groups in New York, all of the lookout for new talent. Her time in Boston, if it is allowed, is the third-fastest marathon ever run by a woman.

Many of Ruiz's answers at the press conference today were greeted skeptically by the reporters, but the angriest questions came from people connected with the running establishment.

"Are you not frauds?" one man shouted at Ruiz and Marek.

Marek, president of the suburban Road Runners in Westchester County, is accused of insisting on starting in the front row of the 1978 New York Marathon, although his best time did not entitle him to do so.In addition, he allegedly rode part of the course in a car before running across the finish line. He was barred by Lebow from further New York Marathon competition, but entered in 1979 under an assumed name, Lebow said.

Ruiz, who was born in Havana and came to the United States in 1961 when she was seven, attended Wayne State College in Nebraska, where she is remembered as having jogged a lot.

She produced the report of a stress test she took Feb. 28 in an effort to prove she is in excellent condition.

Bob Glover, a fitness consultant who attended the press conference, said the stress-test figures, while not absolutely conclusive, tended to show Ruiz is not in shape to run a marathon. For example, her resting pulse rate was given as 76 while a serious runner's would be much lower, Glover said.

Even those who don't believe Ruiz agree with her on one thing. She has predicted that there will be more attention paid to women runners in future races.

Her next race, she said, will be a 10-kilometer race in July that is being organized by Marek. She can be sure of close observation.