Frank M. Snowden Jr. didn't set out to become the foremost American authority on blacks in the ancient world. He says he stumbled into this rarefied world of classical study by happenstance.

It happened while he was writing his Harvard doctoral dissertation on slaves and freedom in Pompeli.

"I wasn't looking for blacks, but I saw the nucleus of further research," he says with a booming laugh. "So I started examining Greek and Roman sources, and later I saw references to Egyptians and Assyrians. Then I couldn't stop. I went through Greek and Roman literature from beginning to end and Christian literature for the first six centuries A.D."

Today, more than 35 years after he received his doctorate, Snowden's book, "Blacks in Antiquity," an account of black Africans in the Greco-Roman world, has become a standard reference work.

And Snowden, chairman of Howard University's classics department, is also the only American to write a chapter for the book, "The Image of the Black in Western Art". He has published many articles and is currently working on a book about blacks in ancient societies from the pharaohs to the caesars.

He also is in constant demand to make speeches on the subject. Today, he speaks at the Hotel Washington to a joint convention of the Classical Association of Atlantic States and the Washington Classical Society, both organizations of teachers, scholars and laymen from all walks of life interested in studying the classics.

Always impeccably dressed, the scholar talked about his research and his findings in a wide-ranging interview while sitting in the study of his Glover Park apartment where books are crammed on every shelf.

For his research, Snowden visited more than 100 museums in Europe, Asia, Africa and this country. Snowden's travel was made easier by him being a State Department lecturer in Africa and Asia, cultural attache at the U.S. embassy in Rome and a U.S. delegate to a UNESCO conference.

"It was difficult. I had a family (two children), I was teaching, I was dean (of Howard's college of liberal arts) and I was trying to write.

"Fortunately my wife was very helpful. She teaches art at Coalidge High School. She drew sketches for me at many museums. My notes weren't enough. Sometimes they'd confuse me."

After his many years of research, Snowden has concluded that, unlike modern societies, the ancient Greeks and Romans did not make race or color obstacles to social integration.

Says the professor: "There were frequent distinctions between slave and free; and, among both Greeks and Romans, often self-congratulation on their achievements but, by far the majority of commentators agrees that nothing comparable to virulent color-prejudice existed in the ancient world."

First encounters with blacks, he says, involved soldiers and mercenaries, not slaves or "savages." On the other hand, the scholar suggests that in 16th-century England the color of the first blacks made such a sudden and powerful impact on the fair Britons that pigmentation became a basis for identification.

Also, blacks and slavery were not synonymous in ancient societies because whites, too, were held in bondage, he explains.

"Why were the Greeks interested in blacks," asks Snowden rhetorically in his crisp Boston accent. "They were new people and so on. But more importantly, it gave them an opportunity to contrast color in their art."

He points animatedly to a plate in the book, "The Image of the Black in western Art," and says: "Look at how the artist represents a black on black background. It was a challenge. A lot of people ask why the Greeks drew blacks. The potters had that magnificent black glaze. Why not use it"

Snowden said it was difficult to say with certainly what conditions or factors may have made ancient attitudes toward blacks more liberal than modern notions.

Even modern sociologists and historians, who have developed elaborate techniques for gauging racial attitudes encounter trouble in determining the attitudes of whites toward blacks, says Snowden.

"There's scholars who imply that the ancients wouldn't have mentioned color if they had been free of color prejudice," he continues. "And there are some who say that Greek artists depicted Negroes as caricatures.

"But there was no stereotyped concept of the Negro as ugly or comic. And when Ethiopians were mentioned, their blackness did not evoke hostility."

The term "Ethiopian," the professor points out, meant "burnt-skinned man" and was the Greeks' designation for all dark-skinned Africans, including black Africans as well as mulatoes.

In early Christianity, says Snowden, the Ethiopian came to symbolize the peoples out of whom the church would grow. 'Moses' marriage to an Ethiopian represents for some the spiritual law (Moses) and the church (the woman) gathered from among the Gentiles, he adds.

Before Snowden's "Blacks in Antiquity" appeared in 1969, he says, no one had attempted to examine through art the role blacks played in the ancient world. Now there are several books available - and more are on the way.

The professor plans to have his second book published in 1979. And the pace is picking up.

Says Snowden: "I've been asked to do film strips. I'd like to do a text book for secondary schools. And after I finish the book on blacks in ancient societies, I'd like to look at how the black presence in antiquity influenced later periods."

He leans back and laughs: "But I only have so much time left myself."