Pediatricians and public health officials are bracing for a major shortage of pertussis vaccine this summer and fall.

"The United States is facing a crisis situation in the next six weeks over the pertussis vaccine," said Dr. Martin Smith, president of the American Academy of Pediatrics in an interview at the academy's annual spring meeting here last week.

Manufacturing delays by one drug company -- Connaught Laboratories Inc. -- have already produced a shortage in the federal government's stockpiles at the Centers for Disease Control in Atlanta. Liability insurance for the vaccine division of the only other U.S. manufacturer -- Lederle Laboratories -- will expire in June, which could place supplies in further jeopardy, Smith said.

Pertussis, also known as whooping cough, is a childhood illness that generally afflicts children under 2. Prior to immunizations, the disease claimed thousands of lives each year.

But today, protection against pertussis begins at 2 months of age with an injection known as DPT, which also provides immunity against diphtheria and tetanus. Children receive four additional booster shots: at 4 months, 6 months, 18 months and between 4 and 6 years.

The CDC in Atlanta has "very, very little DPT vaccine," said Dr. Alan Hinman, director of the CDC's immunization division. The reason, Hinman said, is a "delay in the manufacture and release of vaccine from Connaught Laboratories," which produces 60 to 70 percent of the vaccine in the United States.

The shortage is expected to worsen this summer and fall, after Lederle Laboratories, which produces 30 to 40 percent of the DPT vaccine for the U.S. market, loses its liability insurance. Experts predict that when the insurance runs out, Lederle will pull its vaccine from the market.

"We have not as yet made a decision about what we will do," said Lederle spokeswoman Martha Homma. "In light of the current liability insurance situation, there certainly is a strong possibility that we will withdraw from the market."

"We're quite concerned about the problem," Hinman said. "What we potentially face is a nine-month period in which basically we would have two thirds of the vaccine that we normally use."

Unlike other childhood illnesses, pertussis cases are on the rise, although this rise is not related to the current vaccine shortage. Last year, the number of American children who contracted whooping cough increased 50 percent from about 2,300 cases reported in 1984 to almost 3,300 cases in last year.

Most recent cases of pertussis, Hinman said, "have occurred in children who are too young to be immunized or should have been and weren't because of economic reasons or competing priorities."

Some of the increase in pertussis may also be accounted for by better diagnosis and reporting of outbreaks, Hinman said. A few cases are the result of "parents making a conscious decision to not have their children immunized."

Like all immunizations, pertussis vaccine has some possible side effects. Approximately one in every 310,000 children who receives the DPT vaccine develops a neurological complication, according to the CDC. Media reports in the past several years depicted poignant stories of children who allegedly experienced such side effects, and those reports may have discouraged some parents from immunizing their children, experts say.

"We know that the vaccine is not ideal," AAP president-elect Dr. William C. Montgomery said in an interview at the annual spring meeting. "But the problems of the disease are much greater than the problems of the vaccine."

In the meantime, officials are also pursuing new vaccines against whooping cough. Scientists at the National Institute of Child Health and Human Development will start clinical trials later this month of a new type of pertussis vaccine, similar to a brand currently used in Japan and Sweden.

This new vaccine "relies upon a single protein, called pertussis toxin, which has been detoxified in a novel manner," explains an NICHD spokesman. "Its mode of action will be similar to our current diphtheria and tetanus toxoid vaccines," and is expected to have fewer side effects than the vaccine now in use.

But even if the trials are successful, experts say, it will be at least two or three more years before the new vaccine could receive approval from the Food and Drug Administration -- too late to help with the current shortage.

Part of the slack may eventually be taken up by increased production of vaccine at Connaught Laboratories. "We do not see any problems with our ability to continue to manufacture DPT," said David J. Williams, a Connaught vice president and general manager. "But it would take us a while to get up to speed, probably a nine-month period before we could supply the whole market."

In the meantime, public health officials do not think that pertussis cases will increase dramatically. "I think there would be very little immediate impact for a couple of reasons," Hinman said. "Since we have a high level of immunization in the childhood population even if we stopped vaccinating entirely, it would still be a year or two before there were significant increases in cases of pertussis."

Proposed legislation could help eliminate future liability problems for drug companies. The National Vaccine Compensation Act, introduced by Sen. Paula Hawkins (R-Fla.) and supported by the American Academy of Pediatrics, the National Coalition of Pediatrics and Dissatisfied Parents Together, would provide no-fault compensation for children who have suffered the complications of immunization. Rep. Henry A. Waxman (D-Calif.) is expected to introduce similar legislation in the House this month.

"I think that this crunch is going to create enough of a public concern and outcry," said AAP president Smith, "that Congress may be motivated to move faster than it's been noted to before."