The pioneer maker of birth-control pills unexpectedly agreed this weekend to pay an undisclosed sum to settle a product liability lawsuit brought by an Anne Arundel County woman whose liver has enlarged to about 24 times its normal size.

The settlement between G.D. Searle & Co. of Skokie, Ill., and Constance Bailey, 46, and her husband Jerry of Severna Park ended a six-week trial after both sides had presented their cases to a jury in Ellicott City, Md.

Bailey's liver, which is believed to weigh 60 to 65 pounds, may be the largest ever found in a human, according to physicians consulted by her lawyers. She has polycystic liver disease, in which tiny cysts proliferate.

Bailey blamed the enlargement on nine years' use of Searle oral contraceptives -- Enovid, the original pill, and Ovulen, which the U.S Food and Drug Administration approved for sale in 1966. The company associated her affliction with a birth defect, emphasizing that the disease was known many decades before the hormonal pills had been invented.

A doctor prescribed Enovid for Bailey in 1963, following the birth of her second daughter, and Ovulen a few years later. Both pills contain mestranol, an estrogen also used in certain other brands, and a progestin.

Howard County Circuit Judge Robert F. Fischer had set closing arguments for this week. The jurors, selected Jan. 13, are to be notified formally of the settlement today.

Joel L. Katz, an Annapolis lawyer who filed the suit for the Baileys five years ago, said in an interview yesterday that William P. Richmond, a Chicago counsel for Searle, made an offer acceptable to the couple Saturday.

At the time, the attorneys were in court to discuss the instructions the judge would give to the jury. Settlement talks had begun 2 1/2 weeks earlier. Katz said the settlement bars disclosure of the amount of money Searle is to pay the Baileys.

Katz noted, however, that he was "planning to ask the jury to award in excess of $10 million" to compensate Bailey for her liver condition and to punish Searle for alleged wrongful conduct. His quest for punitive damages involved plaintiff's expert M. Adrian Gross, who was the FDA's associate director for preclinical investigations until 1979.

In three days of testimony a month ago, Gross charged that Searle gave the agency "false" and "misleading" information about the pills' effects on animal livers. Searle did not call a witness to refute him.

Katz speculated that if the jurors -- eight women and four men -- would have found for the Baileys, they likely would have awarded punitive damages. He speculated that the possibility of punitive damages influenced Searle to make the settlement offer.

Richmond has declined from the start of the trial to talk with reporters.

Bailey is secretary to an Anne Arundel County circuit judge, and her husband is a salesman for a computer equipment firm in Columbia.