Anew type of whooping cough vaccine looks promising in field studies but still might fall short of protecting children against the disease as well as the vaccine currently on the market in the U.S., Swedish researchers reported yesterday.

At a two-day conference on the new vaccine at the National Institutes of Health, Swedish researchers said that two versions of the whooping cough -- or pertussis -- vaccine were tested at 13 sites for about 15 months. Some 3,800 children, ages six months to 11 months, participated in the study, which was sponsored by the NIH.

The two vaccines "protected against whooping cough, but the protection was not complete," said Dr. Patrick Olin, head of Child Health Services at Fachs Children's Hospital in Stockholm and an investigator of the study.

The new vaccines are called acellular vaccines because they contain only parts of the bacteria that causes pertussis. The main advantage of acellular vaccines is that they cause fewer side effects than the current whole-cell vaccine, which contains the entire pertussis bacteria.

Some children -- the American Academy of Pediatrics estimates 70 to 75 each year -- have severe reactions to the whole-cell vaccine. In rare instances, the vaccine causes permanent brain damage and death and has triggered major increases in liability insurance for pertussis vaccine manufacturers and consequently higher costs to the consumer. The risks associated with the current vaccine have also prompted the research into finding a safer pertussis vaccine.

In Sweden, children have not been routinely vaccinated against pertussis since 1979, when public health officials decided that the cellular vaccine was too risky. The number of cases of whooping cough has increased every year since then.

In the Swedish study, the acellular vaccines seemed to be less effective than the whole-cell vaccine but appeared to lessen the severity of the disease in those children who did develop whooping cough.

One type of the new vaccines protected 55 percent of the children who received it, Olin said. The other acellular vaccine protected about 70 percent of the youngsters who were immunized with it.

Pertussis, or whooping cough, generally lasts for about 1 1/2 to two months. The most dangerous period occurs from the second through the fourth weeks of the disease. During this stage, children with the illness are wracked by uncontrollable coughing so severe that it cuts the amount of oxygen available to the brain and can cause permanent neurological damage. Lung damage is often another permanent side effect of the disease. Before children were widely vaccinated, the disease claimed several thousand lives each year.

"The important and interesting finding is that both vaccines were more protective against the severe form of the disease, about 80 percent effective," said Olin.

For example, 40 of the children in a control group for the study, which received no vaccine, contracted whooping cough. The majority -- 32 children -- got a serious form of the disease, which lasted more than 30 days, and "quite a few of them had the disease for more than 60 days," Olin said.

By comparison, 27 children who received one of the new vaccines contracted pertussis. But only nine to 10 of those children had the disease for more than 30 days, Olin said, "and none had it for more than 60 days." Among the third group of children, which received the most effective form of the new vaccine, only 18 youngsters contracted whooping cough, and only 10 of those youngsters had the disease for more than 30 days.

It seems, Olin said, "that the acellular vaccine moderates the course of the illness, which makes the illness less distressing for the child and the family if they are not completely protected."

Researchers and public health officials in the United States and Sweden are still debating whether the new vaccines can replace the current pertussis vaccine, which has come under fire for its side effects.

"We've all been watching this study closely," said Dr. James Strain, executive director of the American Academy of Pediatrics.

Based on these latest results, Olin said, half the children in the study will be offered booster shots of the acellular vaccine in the fall. It may be, he said, that the new pertussis vaccine could be given every five to 10 years, the way tetanus shots are given now to children and adults.

But whether that will be enough to protect children -- and to reduce the rising number of cases of pertussis in certain countries -- is still not known.

In the United States, 1,730 cases of pertussis were reported to the Centers for Disease Control in 1980. In 1985, the most recent figures available, 3,589 cases were reported. "This is most worrisome," said AAP's Strain.

The quest for a new and improved pertussis vaccine comes at a time when there is concern that the number of American infants being immunized against this and other diseases is dropping. In December, the Children's Defense Fund released a report that noted that the "immunization rates of American children are stagnating over all and even declining for some crucial age groups."

Based on CDC figures, the number of 2-year-olds who are fully immunized against polio, rubella, measles, mumps, diphtheria, tetanus and pertussis dropped from 1980 to 1985 -- the most recent year for which figures are available. In 1980, for example, about 81 percent of 2-year-olds were protected against polio, but in 1985, only 77 percent had been immunized.

Protecting the preschool child is "what we are most worried about," said AAP's Strain. All states require some immunizations for children entering school.

The reason some children are not being immunized is the cost of the inoculations, fueled in part by soaring liability insurance costs. "There are no shortages of vaccines," says Strain. "But the middle- and lower middle-income groups . . . are finding it difficult to afford the cost of vaccines." The indigent and poor are eligible for immunizations at public health clinics. Children who suffer adverse reactions from immunizations can now get help from the National Vaccine Compensation Act, which went into effect on Jan. 1. Under the new law, a trust fund has been established to compensate children and their families who have adverse effects from vaccines, particularly the pertussis vaccine.

For a while, the cost of vaccines will continue to rise because the new law places a surcharge of $4.56 on each DTP (diphtheria, tetanus, pertussis injection) and a $4.44 surcharge on each MMR (mumps, measles, rubella) injection.

The money will be pooled in the trust fund and allocated to up to 150 children a year who suffer adverse effects from being immunized. (The American Academy of Pediatrics estimates that 70 to 75 children a year will actually be affected, but the law provides for twice that number of victims.) The minimum payment to each child is $250,000. But if parents choose to accept the assistance of the trust fund, they must sign away their right to pursue further action in the courts.

During the next several years, the Vaccine Act is expected to reduce the liability insurance costs for vaccine manufacturers, which in the long run is expected to gradually lower the cost of immunizations.

But the changes won't come in time to meet the surgeon general's immunization goal of having 90 percent of all 2-year-olds in the United States fully immunized by 1990. "We're not going to make that," says AAP's Strain.

Nor is it likely that the nation will meet its goal of eliminating measles by 1990, says Dr. Alan Hinman, coordinator of the National Vaccine program at the CDC.

What's more, targets for adult immunizations for a type of pneumonia, pneumococcal polysaccharide, and for influenza also probably won't be met, says Hinman.

But there is at least one success story in the news on vaccines -- one goal in the surgeon general's immunization program that is on target, according to Hinman.

"Rubella {German measles} will be eliminated by 1990," he said.