A million dollars for the Kennedy Center, $800,000 for the Corcoran Gallery of Art and $250,000 for National Public Radio are among the $21.85 million in challenge grants announced yesterday by the National Endowment for the Arts. All the grants will have to be matched three-for-one by the recipients during the next three years.

NEA Chairman Frank Hodsoll said yesterday at a press conference that the grants would go to 50 arts organizations, 15 of which have never before had a grant from the arts endowment.

Marking the endowment's 20th anniversary, Hodsoll introduced Roger Stevens, the first chairman of NEA, who now is chairman of the Kennedy Center. Stevens said the center's grant, its first, will go "to start an endowment for the Kennedy Center. We've never had one. It's a nice boost." To Hodsoll and Jeanne Butler Hodges, NEA's director of challenge and advancement grants, Stevens said, "It's harder to give money away than seek it. It takes great skill."

Corcoran Director Michael Botwinick said the gallery's grant, when matched by other donations, would almost double the Corcoran's existing $3 million endowment. The interest from the endowment would go to fund Corcoran acquisitions and programs.

The grant to National Public Radio, NPR President Douglas J. Bennet said, will give public radio a cash reserve fund to extend its ability "to deliver innovative, high-quality arts and performance radio programming." Bennet said the grant "recognizes, encourages and rewards . . . sound financial management."

Hodsoll said 571 arts organizations in 47 states, the District of Columbia and the Virgin Islands had benefited from more than $1 billion raised to match NEA grants in the eight years of the program. Challenge grants, Hodges said, are aimed at building endowments and lasting improvements.

Other 1985 $1 million grants (at the top of NEA's scale) will go to the Houston Grand Opera, the San Francisco Opera Association, the Boston Museum of Fine Arts, the St. Louis Symphony Society and the Philadelphia Orchestra Association.

Among the 15 first-time grant recipients are the Cooper Union for the Advancement of Science and Art in New York City, $700,000; the Museum of Contemporary Art, Los Angeles, $500,000; the New York Public Library/Performing Arts Research Center, $500,000; and the Abby Aldrich Rockefeller Folk Art Center of the Colonial Williamsburg Foundation, $250,000.