The American Film Institute Theater's major summer series, a retrospective devoted to love stories, begins Friday. The range of programmer Michael Clark's eclectic selections may be gauged by the first two movies scheduled: Luis Bunuel's "El" at 6:30 and Vincente Minnelli's "Father of the Bride" at 8:30 p.m. Incredibly, Clark tops himself on Monday, June 27, with a highbrow-lowbrow one-two punch of "Ordet" and "A Date With Judy."

The 96 titles in the series will be augmented as the summer progresses by compact retrospectives devoted to Buster Keaton, Montgomery Clift and cinematographer Karl Struss, whose still photography will be the subject of an exhibit at the Phillips Collection from July 9-31. Struss himself is scheduled to introduce a showing of one of his most famous credits, "Sunrise," directed by F. W. Murnau, at the AFI Theater on Saturday, July 9, at 6 p.m.

Japanese movie freaks can rally around the Biograph, which has announced a 30-film retrospective beginning Wednesday, June 29, with a double bill of "Ceremony" and "Boy," two earlier features by Nagisa Oshima, whose new picture, "In the Realm of the Senses," will open a few days earlier. Akira Kurosawa is the best represented filmmaker in the series, followed by Okamoto, Ozu, Inagaki, Kobayashi and Mizoguchi. Nothing by Kon Ichikawa, unfortunately.

The remaining double-bills in the series, which concludes Thursday, Aug. 4, will be "Sword of Doom" with "Samurai Assassin," "Tokyo Story" with "An Autumn Afternoon," "Drunken Angel" with "Hoodlum Soldier," "Yojimbo" with "Throne of Blood," "High and Low" with "The Bad Sleep Well," "Chusingura" in its entirety, "Seven Samurai" with "Sanjuro," "The Lower Depths" with "I Live in Fear," "Late Spring" with "Equinox Flower," "Woman in the Dunes" with "Ikiru," "Harakiri" with "The Assassin," "Samurai Trilogy," "Zatoichi Meets Yojimbo" with "Zatoichi's Fire Festival," "The Life of Oharu" with "Princess Yang Kwai Fei" and "Kill!" with "Samurai Rebellion."

The Washington Community School of Music has announced a fund-raising showing of "Leadbelly" on Thursday, June 30, at the Ontario at 8 p.m. A wine and cheese party will follow the showing, and ticket purchases are tax-deductible. For further information, call 526-5737 between 10 a.m. and 5 p.m. weekdays.

The American Film Institute is accepting applications for its next series of grants in the Independent Film-maker Program, funded by the National Endowment for the Arts. Proposals for any type of film project in 16mm or 35mm should be submitted to the AFI, 501 Doheny Road in Beverly Hills, Calif., before Sept. 15 for grants to be announced next January. Grants are made to individuals in amounts ranging from $500 to $10,000.

"Star Wars" tailed off marginally at the box-office in its second week at the Uptown, dropping from $94,922 to $90,517. With District schools beginning summer vacation this week and the suburbs following next week, it appears that the third and fourth week could surpass the $100,000 mark. After six days of the third week, "Star Wars" had grossed $87,559, and the management expected Tuesday's figures to exceed the Monday take of almost $12,000.