At the Animal Rights rally on the steps of the Capitol Sunday, five writers, four movement activists, three pop singers, two actresses, a cartoonist, a professional basketball player and the mayor of Aspen are scheduled to speak about the evils of using animals in medical research.

But there won't be any scientists on the agenda of the protest, which organizers said could attract up to 20,000 people. {Map of march route on Page D6.}

Indeed, on the eve of the largest and most publicized event in the history of the U.S. animal rights movement, the scientists who use animals in experiments and the activists who oppose the practice may have never been so far apart.

On Thursday, flanked by representatives of the nation's major medical research groups, the government's top health official set the tone for the debate by labeling the protesters "terrorists" intent on disrupting valuable science through "intimidation and even violence."

Animal rights activists countered by calling the remarks of Health and Human Services Secretary Louis W. Sullivan "absurd" and "appalling."

At stake in the debate is how a large chunk of the dollars allocated to biomedical research in this country are spent. According to the American Association of Medical Colleges, for example, U.S. medicals schools are forced to spend millions of dollars that otherwise would go for research into responding to tough new animal care guidelines and buttressing security to protect laboratories against animal rights protesters.

If the animal rights movement is successful in getting new restrictions on the use of experimental animals, medical schools will spend more on animal care.

The controversy also has brought into conflict two apparently irreconcilable ideas of how medical research should be conducted and what constitutes ethical science.

For animal rights activists, scientists have been too slow to adopt alternatives to traditional animal experiments. Computer models, sophisticated cell culture screening systems and human subjects, they said, could be effective substitutes for the laboratory animals scientists use in everything from AIDS vaccine research to cancer testing of new chemicals.

The idea of eliminating animals has gained ground in recent years as animal activists have become more outspoken and advocates of animal rights have linked up with the environmental movement.

"We've grown like gangbusters," said Ingrid Newkirk, national director of the Rockville-based People for the Ethical Treatment of Animals, one of the march organizers. "In 1980 we had five members. Now we have 300,000."

But researchers argue that to understand properly how a specific biological process works or whether a given drug is effective, computer programs and test tube techniques are not sophisticated enough.

"Consider research on understanding the relationship between stress and disease," said National Institutes of Health researcher Richard Nakamura. "I can't conceive of doing stress research in a petri dish. It requires a whole organism with a brain in order to understand that relationship."

"Many of the problems that we seek to address depend on a highly structured organization," said Michael Jackson, dean for research at George Washington University. "Diabetes, for example, can be regarded at one level of certain cells or parts of cells. But if we want to understand the entire problem we have to look on it as a multisystem disorder that affects tissues and organs like the brain, the liver, the heart and the kidney. And there is no way that a computer or an isolated cell system can simulate the organization of a tissue or organ."

"One of the really significant observations that can be made in relation to the animal rights movement is that there is not a creditable investigator who supports it," he said. Animal rights activists "are speaking from an unauthoritative position."