A majority of American adults do not know that humans evolved from animal species or that the Sun and Earth are in the Milky Way galaxy. And one-third think that humans and dinosaurs existed at the same time, according to a new nationwide survey on scientific literacy among adults.

The survey, conducted by Louis Harris & Associates and the American Museum of Natural History and released yesterday, found that despite years of efforts to improve science education in public schools, American adults possess a low level of literacy in science.

"The message here is clear and simple," said Ellen V. Futter, the museum's president and a former president of Barnard College. "Americans do not know enough about science or the scientific process."

The survey portrayed an adult population with such a limited understanding of science that only 21 percent of the 1,225 adults questioned scored 60 percent or better on 20 questions that examined basic knowledge of subjects that included space, earth, the environment, animals and causes of diseases. 'Erratic' Grasp of Science

In assessing the findings, Ms. Futter said American adults "seem to have an erratic, almost idiosyncratic" understanding of "bits of science information."

The respondents seemed to score best on questions with an immediacy in today's world. A vast majority, 78 percent, knew that AIDS is caused by a virus. And, questioned within weeks of the last California earthquake, most respondents knew that the continents move.

But more than half did not correctly answer a question on evolution that was asked in these two different ways:

*Human beings developed from earlier species of animals, true or false?

*Human beings evolved from earlier species of animals, true or false?

Forty-six percent said false to both. The survey did not address whether religious beliefs might have affected the result.

Sixty-five percent did not know how many planets are in the solar system, and only a fraction, 10 percent, could correctly name what scientists believe to be the nearest modern-day relative of Tyrannosaurus rex from a list of four: chicken, crocodile, elephant and lizard. (It is the chicken.)

The survey was conducted by telephone in February and March and had a margin of sampling error of plus or minus three percentage points.

The findings are similar to other specialized surveys of what Americans know, like one on geography two years ago sponsored by the National Geographic Society and one last year on knowledge of economics.

And last September, a sweeping study by the United States Department of Education concluded that a large percentage of the American adult population has large gaps in basic knowledge, from an inability to read at all to an inability to read a utility bill. Results to Help Museum

Ms. Futter said the museum would use the survey's results to better tailor the museum's science education classes for adults and children alike. She said she hoped the findings would also be used by community colleges and science organizations to fine-tune existing science education curriculums or begin new efforts to address results that Ms. Futter and other museum officials called "surprising," given the flow of resources into science education into public schools since the 1957 launching of Sputnik by the former Soviet Union.

She and other museum officials said schools alone should not be blamed for the low level of science literacy. Although a four-year study released last October by the American Association for the Advancement of Science called for better curriculums and improved teaching, American students continue to lag behind European and Asian students in achievement tests, a trend that not surprisingly surfaces in the adult population.

Chart: "QUIZ: Testing Scientific Literacy" shows how a national sample of 1,225 adults answered various questions on a test of scientific literacy. (Sources: Louis Harris and Associates, The American Museum of Natural History)