Herman J. Viola could smile. Even as his book, "Diplomats in Buckskins," a history of Indian delegations to Washington, came out, some 500 Indian leaders from at least 150 tribes all over the country were descending on the city to lobby for budget changes.

"It's a very old tradition," he said. "Of course, it's very difficult in spirit today."

For one thing, this week's conference was no tightly orchestrated tribal delegation but a fairly spontaneous movement. First, the Oklahomans started arriving, leaders of many of the 100 tribes living in what was once Oklahoma Indian Territory, from Osage to Cherokee, to be feted by the Oklahoma State Society, congressmen and others in a reception on the Hill yesterday. Then the Crows showed up, and other members of the National Tribal Governments.

By yesterday, with 22 Indian organizations sponsoring the conference, dark men with long black braids were sitting around the lobbies of a dozen hotels.

Also, this group was a far cry from those 19th-century delegations that came here, or were brought, so that the Greatr White father could impress the Indians with the vast numbers and power of the invader they were still resisting.Many refused to believe there could be that many people, insisting that the crowds were being moved from city to city in Potemkin Village style.

For some Indian delegates it was a traumatic experience, ending either in greatly increased local prestige or in disgrace (in 1855 furious Chippewa killed and ate the carriage horse that had borne off Chief Flat Mouth because they thought he had sold them out) or in sickness and early death.

"Many ailments affected the delegates," Viola writes in his fascinating account (Smithsonian Institution Press 1981), "but the two most mortal seem to have been smallpox and pneumonia." One delegate of 16 lost nine members. And the Indian agents often failed to report deaths en route, possibly becaue they felt they might be blamed."More likely, their omissions indicate the general low regard whites of that era had for Indians as human beings."

Easterners in those days seemed curiously remote from the bloody events in the West. In 1877, just months after Little Big Horn, some Poncas were wined and dined here in great style. True, most Americans then knew the hostiles from the peacefuls. But in 1888 Chief Big Foot had his picture taken here in a white man's dark suit with a peace pipe on his lap. Two years later he was photographed again: frozen in the snow, murdered at Wounded Knee.

Over the decades, the Indian visitors grew steadily more sophisticated. Red Cloud came here a dozen times, getting a certain name for himeslf among his Oglala Sioux as a company man. His rival, the great leader Crazy Horse -- the real brains behind Little Big Horn, some say -- scorned him as he scorned all who dallied with the white men and accepted their wool suits and blankets and eager promises.

Still, there were some great moments for the delegates. Yankton Sioux, dazzled by a ballet performance at the National Theatre, threw their war bonnets onto the stage at the feet of a Miss Nelson, the Mountain Sylph. Next day they stopped traffic as they were driven around town in open cars, wearing full military uniforms wiht silver epaulets -- and Miss Nelson's ostrich plumes in their hatbands.

Washingtonians thought nothing of dropping in on the Indians at their hotels, gawking through the open doors (closed rooms gave the visitors claustrophobia) and dogging them through the streets. There was so much drinking, even though it was a crime to serve Indians liquor in their own country, that Viola suggests "this liberal use of alcohol by Indian Visitors to Washington should raise questions about the validity of several important treaties negotiated with them."

He adds: "Even if alcohol were not a factor, one has to question the legitimacy of treaties arrangeed in Washington between government officials and Indians on their first visit to a large urban area. The culture shock alone could have impaired judgments without the additional confusion caused by the limitations of the interpreters, the desire of the Indians to please hosts seemingly so generous and hospitable, and the probable inability of the delegates to comprehend fully, under the best of circumstances, the ultimate significance of the agreements."

As Black Hawk put it: "They might buy our bodies for dissection, and we would touch the goose quill to confirm it, without knowing what we are doing."

Despite the hazards of Washington, the visits became an important factor in Indian tribal life. One eloquent chief said, "Before the white man came the Indian had the buffalo and the buffalo gave them everything they needed, food, shelter, clothing. The white man came and took the buffalo away, but he gave the Indians the government and now . . . that is their buffalo."

The book details even the bills run up by the guests ("Chiricahua Charlie -- suit and shirt . . . $13") and covering a period from Colonial days to the present. The 1972 takeover of the Bureau of Indian Affairs Building by some 500 activists led by the American Indian Movement is omitted, however: Viola says he was persuaded that this was not exactly a delegation. He had hoped to subtitle the book "From Invitation to Confrontation."

The pictures tend to be a somewhat formal, for -- like the Indians' side of the story -- they are hard to come by. The author plans a photo book on the subject if he can dig up more shots of the Indians at play in the eastern cities.

"They were taken, I'm sure of it," he says. "Indians at the ball park, Indians at parties . . . I'm positive they're in people's attics right this minute."