Three pharmacists formerly employed by the nation's largest mail-order prescription service told a Senate subcommittee yesterday that it filled drug orders at such a dizzying pace that they constantly feared for their patients' safety.

Testifying in anonymity from behind a screen, they told the Governmental Affairs subcommittee on governmental efficiency of being pressured to check prescriptions at the rate of one a minute, of technicians who placed the wrong drugs in dispensing bins and of a company that refused to hear their complaints.

"It was a suicidal job. I dreaded if I was going to kill someone or kill myself professionally," said one of the druggists who said she finally quit in disgust.

Officials of the company, which operates a major drug plan for federal workers and retirees, denied the charges and accused the subcommittee of sponsoring a "roadshow" produced by the nation's retail druggists in an effort to discredit mail-order drug sales.

Martin J. Wygod, chairman and chief executive officer of the fast-growing Medco Containment Services Inc., said his firm's safety record and that of others in the industry "far exceeds that of the retail pharmacies." He said his firm, which handles drug sales for many U.S. employes covered by Blue Cross and Blue Shield plans, has seen its sales leap to $400 million a year from $25 million three years ago.

Sen. Jim Sasser (D-Tenn.), presiding over the four-hour hearing, appeared largely unmoved by the company's defense. He conceded that some of the errors attributed to Wygod's New Jersey-based firm and its chain of mail-order drugstores "may be a rare occurrence."

"But I'll just have to tell you that some of the testimony gives me pause," he said, suggesting that the mail-order drugstores might want to consider some form of federal regulation to protect their image.

What Sasser said troubled him most was the testimony of a Virginia Beach woman, the wife of a retired Navy civil servant, who told the subcommittee how the company mistakenly sent her a blood thinning agent instead of the medicine she needs for hypertension.

If she had taken the pills, she could have been placed in a "life-threatening" condition, a Virginia Beach druggist who discovered the mix-up told the committee.

Outside the committee room, Winifred W. Owens said what attracted her to mail her prescription to Medco's National Rx Services subsidiary in Florida was the price. As a Blue Cross subscriber, she was able to get for $5 a 90-day supply of a drug that had cost her $90.

Under a program that became effective this year, Blue Cross and Blue Shield are offering federal workers prescriptions by mail at that price or reimbursement of a percentage of their drug costs after a $250 deductible.

That provision has stirred a storm of controversy among the nation's retail druggists, and their representatives were on hand yesterday challenging the mail-order stores at every turn and boasting of public opinion polls that give druggists high ratings.

Lonnie F. Hollingsworth, president of the 30,000-member National Association of Retail Druggists, attacked Blue Cross for denying federal workers "the freedom to obtain prescription drugs from the provider of their choice" and accused the mail-order houses of dispensing drugs "from a Twilight Zone," where he said they were largely unregulated.

That brought a spirited response from Medco's Wygod, who said his firm is closely regulated by state authorities in the six states where it has sales outlets. He said the company handles 220,000 prescriptions a week with few complaints and accused the subcommittee of focusing on "one dispensing error made six months ago . . . . The error could have happened in any retail pharmacy setting as well," he said.

Owens said outside the hearing room that she has returned to her neighborhood pharmacy despite the higher price. "I'm not ready to die," she said.