PHILADELPHIA -- The stern face of C. Everett Koop, the former U.S. Surgeon General, appears on the television screen. "When I was born, there was no vaccine for polio. No antibiotics. No way to treat diabetes or heart disease," he says. "As a result, our life expectancy was just 52 years."

"Today, thanks to animal-based research, that figure is more than 72 years. Which means that even those against animal research will live to protest 20 years longer."

Koop fades away. "Know The Facts About Animal Research" appears on the screen in large letters.

Thousands of copies of this and other 30-second public-service announcements have been distributed to television stations around the country in recent weeks. The videos are part of a major public relations campaign by the Foundation for Biomedical Research, a nonprofit scientific group, seeking to convince the public of the need to use animals in research.

The effort is one example of how the scientific community has mobilized to aggressively counter the assaults of animal-rights activists. After sitting quietly on the sidelines for most of the 1980s while animal-rights activists gained support, researchers now are seeking to negate the activists' arguments.

"We can't hide our heads in the sand any longer," said Robert L. Barchi, director of the Institute of Neurological Sciences at the University of Pennsylvania. "The animal-rights community is beginning to have a tremendous impact on how science is conducted in the country."

Angered by more than 70 physical attacks against research facilities in the last eight years and the theft of more than 2,900 animals, top officials at the National Institutes of Health, the Department of Health and Human Services and other federal agencies have angrily denounced the activists' tactics.

Fearful that proposed animal regulations will make biomedical research prohibitively expensive, scientific groups have lobbied Bush administration officials to postpone adopting these rules.

In recent months, scientific groups have held news conferences, distributed white papers, conducted workshops at scientific meetings and taken other steps to counter the growing strength of the animal-rights movement.

As a result of these efforts, animal activists have escalated their own activities.

Several animal groups have begun raising funds for "war chests" to pay for public relations and advertising campaigns of their own. A massive "March for the Animals" demonstration was held June 10 in Washington. Activist groups have expanded their educational efforts and conducted strategy sessions to discuss possible courses of action.

"The debate over the use of animals is maturing," said Bernard Unti, vice president of the American Anti-Vivisection Society in Jenkintown, Pa. "Both sides realize that it has now become a battle over public opinion."

Many scientists now concede that their past strategy of keeping a low profile in the hope that protests against laboratory animals represented just a passing fad was an error.

In the absence of effective counter-arguments, the animal-rights movement has grown from being a fringe element into a potent political force. The American Medical Association estimates that there are now more than 400 animal-protection groups in the United States with a combined budget of more than $200 million.

Membership in one of the most militant groups, People for the Ethical Treatment of Animals (PETA), has soared from a handful of people in 1980 to more than 300,000 today. The organization now has a paid staff of 85 and an annual budget of more than $7 million.

PETA and other groups have waged successful campaigns to shut down animal experiments at the University of Pennsylvania, the University of Cincinnati, Louisiana State University and other universities. Activists were successful last year in persuading Avon, Revlon and other large cosmetic firms to stop testing their products on rabbits and other animals.

These successful efforts worry many scientists who fear that vital biomedical research projects could be shut down. To counteract these campaigns, the following actions have occurred in recent months: The Society of Neurosciences, the American Association for the Advancement of Science and other professional groups have conducted special symposia on how to combat the arguments of animal activists. Top officials at Penn, New York University and other universities have held news conferences before animal-rights demonstrations on their campuses to make sure the media hear their side of the story. On various university campuses, hundreds of scientists have demonstrated against lecturers who oppose the use of animals in research. At one session last month, Penn scientists dressed in white lab coats and carried placards outside the meeting room. In hospital waiting rooms, posters supporting the use of animals in biomedical research have been tacked onto bulletin boards. Educational material has been distributed to schools. And white papers explaining the need for animals in research have been mailed to journalists and legislators.

"The time for apologetic tones is past," said Frederick K. Goodwin, administrator of the federal Alcohol, Drug Abuse and Mental Health Administration in Rockville, Md. "This is not a movement with which one strikes compromises."

Most scientists say they are not opposed to animal-protection groups that seek to improve the treatment of laboratory animals. But they do oppose animal-rights groups that they say are seeking to completely halt the use of animals in scientific research.

"They have started with scientists because we are most vulnerable," said Alan Rosenquist, an anatomy professor at Penn. "But their real agenda is to halt the use of all animals by people. They are also seeking to shut down zoos, circuses and the meat and dairy industries."

James O. Mason, an assistant secretary for health, said that animal-rights activists had caused millions of dollars of damage, set back important research and intimidated scientists into giving up biomedical projects. One of the most recent break-ins occurred in January, when activists ransacked the offices of Adrian Morrison, an anatomy professor at Penn's School of Veterinary Medicine.

Suzanne Roy, a spokeswoman for the Physicians' Committee for Responsible Medicine, a group searching for alternatives to the use of laboratory animals, said that efforts to portray all animal activists as terrorists would not be successful.

"The animal-protection movement has 10 million Americans as members, including thousands of physicians," she said. "The scientific community is going to find it very difficult to portray this group as a bunch of radicals."

Supporters of the use of animals in research argue that important discoveries made in treating heart disease, cancer, poliomyelitis, diabetes, smallpox and other diseases have involved the use of animals. Since 1901, about two thirds of the Nobel prize winners in physiology and medicine have used animals in their research.

Most animal activists do not dispute these claims, although some say the importance of animals in these discoveries has been exaggerated. They argue, however, that most of the improvements in people's life spans and health have occurred because of improved sanitation and better nutrition.

Roy said that the development of tissue culture techniques, imaging devices, computers and other devices had greatly reduced the need to use animals in research. "There is no longer a need to use animals to test polio vaccines," she said. "We can safely test them using cell cultures."

But Mason said that regardless of what alternative techniques were developed, there would always be a need to use some animals in research. "We don't want to put a vaccine into children that hasn't been tested in an animal," he said. "I don't want a vaccine tested only on a computer model put into my grandchildren."