More than 80 homeless "street people" quietly moved into the National Visitor Center adjacent to Union Station last night and bedded down on foam rubber mats in a unique and delicately forged agreement with the federal government.

The street people, some dressed in ragged winter coats, filed into the high-ceilinged main gallery of the center about 10 p.m., ate a meal of roast beef, potatoes and succotash prepared by volunteer workers and lay down on rubber mats placed in neat rows.

Their arrival, planned and announced weeks ago by organizers in the Community for Creative Non-Violence, a radical Christian group, was observed by a large contingent of city and federal officials, church volunteers and the press.

Few police were present for the novel experiment in using the Visitor Center as an emergency night shelter for the homeless.

Interior Department Secretary Cecil D. Andrus, whose National Park Service is responsible for the center, was kept informed of developments and had ordered that the street people be accepted courteously.

Everything appeared to work smoothly the first night, but the program's future is uncertain.

The street people, tucked behind a wooden partition and not visible to train passengers passing through the Visitor Center, were expected to leave about 7 o'clock this morning. Organiazers expect greater numbers to return tonight.

CCNV workers have said they plan to stay at the center all winter or until the city provides adequate shelter elsewhere for hard-core street people.

CCNV contends that an undetermined number of street people -- perhaps 1,000 or more -- are so alienated that they will not or cannot use emergency shelter already available at city and church facilities.

CCNV says many street people distrust the formalities and regimentation of conventional shelters.

The National Park Service says that use of the center by the street people is a technical violation of the law and that their stay must be "very temporary."

Interior officials acknowledge that they bowed to CCNV demands in avoiding a confrontation and possible mass arrests of homeless people. The officials now are banking on city welfare agencies to come up with alternate shelter sites that will meet CCNV's approval.

In a carefully worded statement issued last night, National Capital Parks Director Jack Fish said, "The Park Service regards the CCNV action as a 'violation of the law undertaken as an act of civil disobedience.' But the service decided to allow their very temporary occupancy" to avoid a confrontation, he said.

Also, Fish said, "our only real alternative is either to lock up a building, which we will not do, or arrest and remove persons from the building."

CCNV member Mitch Snyder said use of the center will help determine exactly how many street people are in the city. Although relatively few came last night, Snyder said he expects many more tonight as word spreads in the streets.

City welfare workers said some people at the Center last night were regulars at the city's Blair emergency shelter for men in Northeast but had come to the center out of curiosity or because it was more convenient to their daytime haunts downtown.

Among officials observing activities last night were Robert Mendelsohn, special assistant to Andrus; D.C. Department of Human Resources director Albert P. Russo and Fred Mohrman, staff director of the House Interior Appropriations Subcommittee.

Mohrman said he was "personally curious" and had not been directed by the subcommittee to come to the center. The subcommittee controls annual appropriations to the National Park Service.

Snyder said in a recent interview that CCNV deliberately chose the Visitor Center as a conspicuous target in a media campaign to dramatize the plight of homeless people.

"We wanted the natural organic centrality" of the Visitor Center, he said.