The movie deal that hunger activist Mitch Snyder signed earlier this year is about to become a reality. Final contracts were signed over the weekend and movie crews will begin shooting the bitter Washington winter exteriors next month for the film tentatively titled "Race Against Winter." The actor portraying Snyder is Martin Sheen, the star of "Apocalypse Now" and a number of other movies, including many made for television. Actress Cicely Tyson will portray a homeless Washington street woman. A number of real Washington street people will be playing themselves in the made-for-television movie expected to be ready late next year.

In signing the movie deal, Snyder and his Community for Creative Non-Violence will receive $100,000, which is in addition to the $50,000 paid last February when Snyder signed the film option contract. The money will go toward the ever-mounting debt at the Second and D streets shelter. The story revolves around Snyder, who stirred the conscience of the country last winter during a 51-day hunger strike.

Producer/scriptwriter Clifford Campion was in town this year interviewing Snyder and several of the street people before writing the script for the movie, which is being produced by Chuck Fries Entertainment Inc. and CBS Entertainment. While the film company will be shooting exteriors here, the interior filming of the shelter will be shot in Hollywood. Susan Davis in the Pink & Blue

It's been a great year and an especially a great month for Washington water colorist Susan Davis. Her highly recognizable pink and blue paintings of Washington and Eastern Shore themes are on the December covers of Yankee and Washington Woman magazines, as well as the current issues of The New Yorker and The Washington Post TV Week magazine.

A Trinity College English major, Davis is a self-taught artist whose soft, nostalgic paintings peopled by tiny whimsical characters were also on the commissioned Christmas cards of developer Oliver T. Carr and former Reagan aide Michael Deaver. The Carr painting is a winter scene of the historic Willard Hotel, which is now being restored for reopening next year. The Deaver card, a signed limited edition, is of skaters on the canal. Davis has also illustrated a children's book, written by Linda Tyler, to be published next year. End Notes

The Andrew W. Mellon Foundation has presented a $1.5 million gift to create a professorship in art history at Yale University in honor of Paul Mellon, who is retiring as a trustee of the Mellon Foundation. Outgoing Yale President A. Bartlett Giamatti announced that the first appointee to the professorship is Jules D. Prown, who for eight years was director of Yale's Center for British Art, which was founded by Paul Mellon . . .

The murder trial of Cathy Evelyn Smith, accused in the drug overdose death of comedian John Belushi, was assigned to a Los Angeles judge yesterday and is expected to begin in the summer. Smith, 38, will be tried on one count of murder and 13 counts of administering illegal drugs to Belushi during the last hours of his life in his bungalow at the Chateau Marmont Hotel on the Sunset Strip in March 1982 . . .