NORFOLK, Va. (AP) _ More than 150 couples who once might have thought they'd never celebrate Mother's Day gathered for a party Saturday with their children conceived through in-vitro fertilization.

The families brought about 175 children who were conceived at the Jones Institute for Reproductive Medicine at Eastern Virginia Medical School. More than 500 children have been born through the institute, the most successful in-vitro fertilization program in the country.

The families are among the lucky few; about 20 percent of the couples who go through the program emerge with a baby. Under the in-vitro process, eggs and sperm are mixed in a petri dish and the fertilized eggs are placed in the uterus.

''I felt I couldn't miss this,'' said Rochelle Foster, 41, of Matawan, N.J., as she held her 1-year-old son, Jonathan, at a picnic on the medical school grounds. ''It's nice to see all the successful people together because when you're actually down for a cycle ... you don't know who's going to be the ones who are going to be successful.''

Mrs. Foster made five attempts to get pregnant in three in-vitro programs before she succeeded on her second try at the Jones Institute.

''I had been trying since 1976 to have a baby,'' she said. ''I didn't think I was going to have a biological child.''

Janet Adams of Chesapeake went through in-vitro fertilization three times before she got pregnant with triplets, 3-year-old Bradley, Travis and Ryan. ''I got my money's worth,'' she said.

Robin and Danny Morris of Weston, Conn., showed up pushing two double strollers that carried their 21-month-old quadruplets - Sabrina, Tyler, Jesse and Paul.

Mrs. Morris, who was the first to deliver quadruplets in the Jones program, said she had always wanted a large family.

''I couldn't go through in vitro four times,'' she said. ''I got it all at once. It was terrific.''

Dr. Howard Jones, the institute's founder, introduced two special guests to the crowd, 7-year-old Elizabeth Carr of Westminster, Mass., the country's first ''test-tube'' baby, and Sarah Smith, a Virginia Beach woman who was the program's first patient. She delivered twins, Ashley and Heather Smith, in 1985 after eight in-vitro attempts.

''I've told them all along that they're very special to their mommy and daddy, that they are miracle babies and that a doctor helped them to be born,'' Mrs. Smith said.

Nash Bilisoly, a Norfolk lawyer, cradled one of the youngest partygoers, 3- month-old Anica Bilisoly.

After four years of trying to have a baby, Bilisoly and his wife, Vickie Bowdoin, succeeded on their first attempt at in-vitro fertilization.

''I don't know if we would have done it again. It's expensive,'' Ms. Bowdoin said. The couple just paid the institute's $6,000 bill, none of it covered by insurance.

''You just have to cross your fingers and hope for the best,'' Ms. Bowdoin said. ''I really think it's a roll of the dice.''

Like other in-vitro parents, Bilisoly and Ms. Bowdoin said they plan to tell their daughter that she was conceived in a laboratory.

''I think I'll have her first formal portrait taken holding her petri dish,'' Ms. Bowdoin said.