Washington collector, scholar and art dealer Thurlow Evans Tibbs Jr., who has championed the rediscovery of many 19th- and 20th-century African American artists in the past two decades, will donate the cream of his nationally acclaimed collection to the Corcoran Gallery of Art.

The gift of 30 works, valued at $1 million to $2 million, is to be announced tomorrow at a news conference. It also includes Tibbs's vast archives and research library, a unique trove that instantly transforms the Corcoran into a major center for the study of African American art, past and present. "There is no other library like this, even at the Schomburg Library in New York," Tibbs said by phone yesterday.

Tibbs, whose family has a distinguished 100-year history in Washington, has seen the Corcoran shift its priorities in recent years. "The Corcoran is trying to reach out to the community and be a city museum," he said. "What my gift does is place one of the nicer private collections in a public museum, so it can be seen, dealt with and researched."

Washington museums have increasingly become major exhibitors and collectors of African American art. The National Museum of American Art (NMAA) took the lead in the past decade after receiving 1,000 works from the Harmon Foundation and more than 200 major items from the Warren Robbins collection (transferred from the National Museum of African Art, which Robbins founded). And NMAA's recent acquisition of the Herbert Waide Hemphill Jr. Collection of American Folk Art added several hundred more works by African Americans. Tibbs has also given photographs to the NMAA.

Tibbs said yesterday that he hoped his gift to the Corcoran, which will be called the Evans-Tibbs Collection of African-American Art, would help attract donations from other private collectors.

Thurlow Tibbs's grandmother Lillian Evans Tibbs, known professionally as Madame Evanti, was the first African American lyric soprano to receive international acclaim. Soon after graduating from Dartmouth College in 1974, Thurlow Tibbs and his sister inherited their grandmother's gracious 1894 Victorian house in the U Street corridor north of Logan Circle. Doing most of the labor himself, he set about turning it into a museum, commercial gallery and archive on African American art and artists from the 18th century to the present.

"I inherited four or five paintings from the family and a strong interest in art, that was about it," Tibbs said yesterday. During the 1980s Tibbs took advantage of low prices on what he called "great examples by people who'd been ignored" and added more than 400 works to the collection. In 1988 the house was placed on the National Register of Historic Places; the same year, the collection went on a national tour sponsored by the Smithsonian Institution Traveling Exhibition Service.

Tibbs, 43, a Harvard University-trained art historian, spoke from Howard University Hospital, where he is being treated for an illness that neither he nor his friends would disclose. "I'm trying to make sure everything is in the right place," he said.

"He wants to resolve his affairs and make this gift to reinforce our interaction in the field of African American art," said Corcoran curator Linda C. Simmons.

The earliest among these paintings, sculptures and works on paper is an 1886 landscape by Grafton Brown, "California Mission"; among the more recent works are examples by Washington artists Lois Mailou Jones, Sylvia Snowden and Renee Stout. In between are such major works as "The Good Shepherd" (1918) by American expatriate painter Henry O. Tanner (acquired by Tibbs's grandmother in Paris from Tanner himself) and Hale Woodruff's "Landscape" (1936). Other artists represented are Huey Lee Smith, Elizabeth Catlett, Romare Bearden, Betye Saar and Raymond Saunders, and the late Charles Sebree and Alma Thomas, both of Washington.

Tibbs's collection has not gone unseen here.

He organized several important exhibitions at the house-museum over the years, including "Surrealism and the Afro-American Artist." In 1983, "Six Washington Masters," featuring works by Richard Dempsey, Lois Jones, Delilah Pierce, James Porter, Alma Thomas and James Wells, helped revive the forgotten careers of several of these artists.

In 1984, another revelatory show brought to light the work of Charles Sebree, who had been overlooked by the Washington art establishment. Sebree died weeks later.

For each exhibition, Tibbs published a scholarly catalogue, sometimes with the help of small grants, more often at his own expense. Until 10 years ago, when the market in these works began to heat up and he was able to make some sales to support his activities, he also held down a full-time government job.

It was last month's combination sale and gift by Tibbs to the Corcoran of a major work, "Into Bondage" (1936) by Aaron Douglas, that launched discussions with curator Simmons and Corcoran Community Coordinator Teresa Grana.

Tibbs describes the Douglas painting -- ships arriving in Africa to pick up manacled slaves -- as "a marvelous art deco journey into racial consciousness."

The Corcoran already owns 60 or 70 works by African American artists, but has never had a focused collection devoted to the subject.

According to Simmons, the works donated by Tibbs will be "mainstreamed" into the Corcoran's American collections; they will also be used in special installations here and in loan shows elsewhere.

Several will go on view July 4 in a special exhibition at the Corcoran. Photographs by James Van Der Zee and Addison Scurlock, also given by Tibbs, will be shown next fall.

"I'm probably going to add more to the Corcoran collection," Tibbs said yesterday.

On Saturday he will receive the Corcoran Medal at Corcoran School of Art commencement ceremonies. The rarely given medal will recognize Tibbs's contributions not only to the Corcoran, but also to the nation's capital. CAPTION:Romare Bearden's "After the Bath" is among the donated works. (Photo ran in an earlier edition) CAPTION:Margaret Burroughs's oil "Still Life" dates from 1943. (Photo ran in an earlier edition) CAPTION: Thurlow Tibbs (shown in his study in 1984) has collected works by African American artists, including the paintings behind him, for many years. CAPTION: Far left, Addison Scurlock's portrait of Tibbs's grandmother Lillian Evans Tibbs. CAPTION: Left, Betye Saar's mixed media installation "Dat Ol' Black Magic." CAPTION: Sargent Johnson's "Singing Saints" is among the African American artworks donated by Thurlow Tibbs.