SAN FRANCISCO (AP) _ A group of parents contends as many as 37 children may have been sexually abused at an Army day-care center, and officials say at least two children have been infected with a sexually-transmitted disease.

Presidio spokesman Bob Mahoney said Monday that more than 60 children have been seen at the Army's Letterman Hospital in recent months after their parents reported they have been be victims of sexual abuse at the center, which cares for 250 children daily.

''There are a number of cases where child abuse has been identified,'' he said, adding that the boys and girls have been undergoing counseling as a result.

Two couples helping to spearhead a drive for a complete investigation of the center are proceeding despite fears that they, like some parents in the McMartin Preschool case in Manhattan Beach, near Los Angeles, will be accused of encouraging children to fabricate stories of molestation.

''We don't want to tie the prosecutors' hands and jeopardize the investigation,'' said Dennis Runyan, an Army dentist who said his two daughters were abused at the center.

''At the same time, we hope to get all the victims identified and we don't feel that's been done yet,'' said Mike Tobin, an Army engineer who said his son was raped at the center. ''We want the children to get to therapists, to get help, so that this doesn't just ricochet around in their heads and snowball. We think there are a lot of children involved.''

The FBI is investigating alleged molestation at the sprawling Presidio Child Development Center for civilian and military personnel at the post at the south end of the Golden Gate Bridge, but would not say when the investigation is expected to conclude.

''It is an extensive investigation. The agents are still conducting interviews and are still collecting evidence,'' FBI spokesman John Holford said on Monday. He declined to comment on the number of suspected victims or the number of children and adults interviewed.

''Specifically, because of the long period of time in which this case concerns itself, we simply don't know how many children are involved,'' said Col. Joseph V. Rafferty, commander of the Presidio.

''We are very confident that the FBI is conducting a very thorough investigation and that when they do go to trial, they will have a very firm case,'' said Mahoney. ''The child care center is a safe place to be, and there have been no new reported cases since the November incident.''

Investigation began last November, after the 3-year-old son of Mike and Joyce Tobin came home from the center and allegedly complained ''Mr. Gary'' had hurt him sexually. The Tobins said a doctor's examination showed the boy had been raped.

Gary Hambright, 33, who had worked at the preschool for 18 months, was charged with sodomy, oral copulation and lewd and lascivious conduct. However, the charges were dropped when a federal judge ruled in March that the child was too young to competently testify, and that the boy's remarks to his mother, nurse, doctor and brother about his alleged abuse were hearsay.

In April, five couples signed a letter sent to 300 families whose children had been cared for by Hambright. It said that authorities had identified 37 children as possible victims of sexual advances.

The Tobins have been joined in their fight for a full inquiry by Dennis and Gretchen Runyan, who say their children also were molested at the center.

In addition, another group of parents who use the day care center last week circulated a petition at the Presidio, calling for a ''town hall'' meeting to discuss the situation.

Parents have contended that four children have contracted the sexually- transm itted disease chlamydia. According to Mahoney, Army officials put the number at two, possibly three. ''One would be pretty disturbing,'' he said.