ALEXANDRIA, Va. (AP) _ An infertility doctor being tried on fraud charges misled a ''staggering'' number of patients through false pregnancies and miscarriages, a doctor who examined his records testified Tuesday.

Dr. Cecil Jacobson ''knew exactly what he was doing,'' said Dr. Mary Damewood, an infertility specialist at Johns Hopkins Hospital.

Judging from Jacobson's medical records, she said, ''He had a scheme outlined to do all of this.''

Jacobson faces 52 counts of fraud and perjury. He is accused of using hormone injections to trick some patients into believing they were pregnant when they were not and of fathering up to 75 children by using his own sperm in artificial insemination while lying about the source.

Another witness, Launi Jean Robertson, who worked as a receptionist for Jacobson from 1982 to 1985, said she became convinced that Jacobson was using his own semen and that sometimes one sample would be distributed among more than one patient.

''There was only a certain amount (of sperm) there and a number of patients coming in,'' she said.

A former lab assistant, Gudrun Slaughter, who worked for Jacobson for eight years, said she also was convinced that Jacobson donated his own sperm and that he sometimes would divide it among more than one patient.

Damewood said she examined records of about 1,000 of Jacobson's patients and found that hundreds of them had been led through a series of supposed pregnancies and miscarriages.

''The number of patients that have failed pregnancies and these basically unheard of reabsorptions was just staggering,'' she said.

Several women have testified that Jacobson convinced them that their bodies had reabsorbed dead fetuses.

''The women in the courtroom were just the tip of the iceberg,'' Damewood said.

Another witness, Vicki Eckhardt, said that she experienced seven supposed pregnancies and miscarriages under Jacobson's care during a three-year period.

Mrs. Eckhardt also testified that Jacobson guaranteed her she would have a baby. The prosecution said Jacobson told the Federal Trade Commission in a sworn affidavit that he never guaranteed to any patient that she would become pregnant.

Other former patients who testified Tuesday included;

- Judith Dowd, who said she was 46 and suffered from blocked fallopian tubes when Jacobson gave her hormone injections in 1987 and then told her she was pregnant.

''He reassured me that the child was proceeding to grow normally,'' she said. Months later, she said he told her the baby was dead and had been reabsorbed into her body. She later sued Jacobson and received a $130,000 settlement payment.

- Susan Dippel, who testified that two days after another doctor told her she was not pregnant Jacobson conducted a sonogram and ''made a point of saying there's no mistaking that fetal heartbeat.''

- Jean H. Blair, who said Jacobson told her six times in 13 months she was pregnant but said later all miscarried. She said she suggested another fertility hormone but ''he laughed it off and told me I had been reading those women's magazines again.''

She said another doctor later prescribed that hormone and she was pregnant within a month.

Damewood said she and a radiology specialist examined a number of sonograms in which Jacobson reportedly pointed out fetuses to the patients. They found no signs of fetuses on the pictures.

''You can't mistake what a fetus looks like,'' she said. ''It must have been clear that these women were not pregnant.''

Jacobson's defense lawyer, James Tate, has repeatedly suggested that the patients may in fact have been pregnant when Jacobson told them they were. Jacobson agreed to stop practicing medicine in 1988 and now conducts privately funded medical research in Provo, Utah.