Hope Clinic for Women Ltd., a yellow, one-story cinderblock building in the heart of this grimy river city, is a creation of the U.S. Supreme Court's 1973 decision legalizing abortion.

It has its own toll-free, long-distance number, its own newsletter, and it regularly advertises in newspapers as an "outpatient surgical center" offering abortion services, female sterilization and birth control information.

The clinic, founded in 1974, is a one-stop abortion center. For $200, a woman who has been pregnant 12 weeks or less can obtain an abortion. The cost jumps to $250 for a woman pregnant 12 to 14 weeks.

The operation takes five to seven minutes, a clinic counselor said today, adding: "You can be out of here in about four hours. It's very safe."

Exactly how many abortions the clinic performs each year is not clear, although anti-abortion groups estimate, based on reports from the Illinois Department of Public Health, that the number may exceed 4,000.

But it is clear that the clinic has provided a good living for its owner, Dr. Hector Zevallos, whom kidnapers held, along with his wife, for eight days until their release Friday. A fanatic anti-abortion group called the Army of God has claimed responsibility for the kidnaping.

No arrests have been made in the case, though the St. Louis Globe Democrat reported today that the FBI was searching for three white men who seized the Zevalloses Aug. 12 at their fashionable home in nearby Edwardsville.

The FBI refused to confirm that report and offered no details in the case today. The Zevalloses, who were released unharmed at 4:40 a.m. Friday, remain in seclusion in their home. At the request of investigators, they are refusing to speak with reporters.

The atmosphere was tense outside the Hope Clinic as dozens of young women arrived early today. An armed security guard hired by the clinic stopped visitors in the parking lot, preventing nonpatients from entering the clinic. Clinic spokesmen refused to meet with reporters.

Four other abortion clinics in the St. Louis area also tightened security.

"We're all terribly frightened by the kidnaping," said Ingrid Smith, executive director of the Ladies' Center, an abortion clinic. "We know we're always in danger. I've had threats on my life before."

Hope Clinic sits behind St. Elizabeth Hospital, a Roman Catholic institution, in this industrial city across the Mississippi River from St. Louis. The location--and the fact that Zevallos, a Catholic, is on the staff of the hospital--has long been a cause of friction.

A group of nurses has set up a service for anti-abortion counseling and free pregnancy testing in a van on a parking lot adjacent to the clinic, and the Rev. Edwin Arentsen, a priest from nearby Addieville, Ill., has been arrested several times for attempting to interfere with the clinic.

The Granite City area is something of a hotbed of anti-abortion sentiment. Phyllis Schlafly, leader of the national campaign to stop passage of the Equal Rights Amendment, lives in nearby Alton; so does Felicia Goeken, executive director of the Illinois Federation of Right to Life.

Zevallos came under attack from anti-abortion groups in 1977 when Barbara Lee Smith, a married 18-year-old, died several hours after having an abortion at the clinic. An autopsy concluded Smith was 14 to 16 weeks pregnant. The face and spinal column of a fetus were found still in her uterus.

With such longstanding tensions, anti-abortionists were immediately suspected when Zevallos, 53, and his wife, Rosalie Jean, 45, disappeared. "He has got a lot of enemies," said Madison County Sheriff Emil Toffant.

Organized anti-abortion groups promptly disavowed any connection with the case. "God does not want the death of a sinner, but that he be converted and live," Arentsen told a reporter.

Anti-abortion activists are bitter that their cause has been linked to the kidnaping. They insist they had never heard of the Army of God before last week when the group claimed to be responsible not only for the kidnaping but also for the firebombing of two Florida abortion clinics.

Letters signed by the group in both instances demanded that President Reagan denounce abortion, something he has repeatedly done.

"This kind of action indicates a frustration level we don't find in our movement at this time. The Senate is debating our legislation," said Ann O'Donnell, chairman of Missouri Citizens for Life. "I feel a little uncomfortable taking this thing on the chin."

In her office in Alton, Goeken, leader of the largest Illinois anti-abortion group, agreed. "Anyone who has any basic knowledge about our movement knows about Reagan's stand on abortion," she said. "He's said time and time again that he's on our side.

"I'm sorry Dr. Zevallos has gone through this strain and trauma," she added. "But I know he's responsible for a lot of emotional trauma himself. Maybe now he can comprehend the trauma women he has operated on go through."