Lederle Laboratories, one of the two manufacturers of a vaccine for diphtheria, whooping cough and tetanus, announced yesterday that it will continue to supply DPT vaccine but will nearly triple its price to combat rising liability problems.

Robert B. Johnson, president of the Wayne, N.J., company, said the company's DPT vaccine insurance coverage runs out on June 30. He said the price hike is necessary to help "self-insure the company for future liability exposure . . . . It is the only way we can remain in the market."

Dr. Martin H. Smith, a Gainesville, Ga., physician who heads the American Academy of Pediatrics, said that the Lederle decision to continue making DPT vaccine "averts a supply crisis" in the immediate future but creates a "cost crisis for all of us" with serious long-term implications.

"It really is a major problem. I don't know whether people will drop out or shift to public sources for it," Smith said. He complained that the "private sector will be carrying the biggest burden."

The government estimates that about 18 million doses of DPT vaccine -- short for diphtheria, pertussis (whooping cough) and tetanus -- are given each year in the United States. This includes three shots in the first year for the roughly 3.5 million newborns, and two booster shots -- at 18 months and just before entering school.

The shots are mandatory for almost all public school students, with about half of the immunizations given in public clinics and half in private physicians' offices, said Phil Horne of the federal Centers for Disease Control.

Horne said that the "federal program should not be affected that much" by the Lederle price jump. He said that CDC has just signed a one-year contract with the other DPT supplier, Connaught Laboratories Inc. of Swiftwater, Pa., at a rate of $3.01 per dose, but there might be a "rebound effect" if more parents go to public programs for their children's shots.

Lederle, considered the major supplier to physicians, said its price to them will increase from the current price of $4.29 to $11.40 per dose, with $8 set aside for product liability. It said that last year 100 lawsuits were filed against the company claiming damages for DPT-related injury, more than the total of the three previous years.

The price in the doctor's office will be higher than the Lederle charge, to cover additional costs of administering the vaccine, said academy president Smith. While it is too early to tell, he predicted that the current average of about $12 per DPT shot may jump to at least $20 to $25, not counting the office visit.

Smith said he expects Connaught to have a similiar price hike for private purchases of the vaccine in the near future. Connaught officials did not return phone calls yesterday afternoon.

DPT vaccine may cause side effects ranging from minor discomfort to brain damage. But government estimates suggest the chance of serious long-term harm is rare -- about one in 310,000 doses -- and that the potential risks are far outweighed by the benefits of preventing these deadly childhood illnesses, Smith said.

He said that the price increases are likely to increase pressure for new vaccine compensation legislation pending in Congress.