THE THEATRE DEVELOPMENT FUND, in its annual report, said it had filled more than 2.3 million seats at theater, dance, and music performances in fiscal 1987-88 through its several programs. This resulted in revenue of more than $38 million for the benefited theaters. Established to encourage the production of new plays and musicals in commercial theaters, the fund runs the TKTS booth in New York's Times Square and operates ticket subsidy and other programs to assist the performing arts, commercial and nonprofit. A MAJOR EXHIBITION OF DRAWINGS by Richard Diebenkorn opens tomorrow at the Museum of Modern Art in New York. This will be the first full-scale survey of the California artist's drawings. Included in the show (through Jan. 10) are watercolors, gouaches, and works in mixed media. The exhibition will travel to the Los Angeles County Museum of Art (March 10-May 14), the San Francisco Museum of Modern Art (June 14-Aug. 27), and the Phillips Collection in Washington, D.C. (Sept. 23-Nov. 26). PILOBOLUS DANCE THEATRE opens a month-long engagement at the Joyce Theater in New York Dec. 13. Four works are scheduled for the opening-night gala, including the New York premi`ere of ``I'm Left, You're Right, She's Gone.'' The company is on tour now, visiting Dallas (Nov. 18-19), Washington (Nov. 26), Thunder Bay, Ontario (Nov. 29), and Knoxville, Tenn. (Dec. 5-6).