TRADITIONALLY the slowest month of the Washington year, August still offers some repertory film delights: * The Biograph Theater begins its seventh festival of Japanese films Friday with a one- week run of Shohei Imamura's The Ballad of Narayama, making its belated Washington premiere after winning the top honors at Cannes in 1983. (Complimentary sushi hors d'oeuvres will be served at the Friday show only.) For a complete schedule of the 18-film festival -- spanning the years 1947 to 1983 and curated by Michael Jeck -- call the Biograph at 333-2696 or drop by 2819 M Street in Georgetown.

* The American Film Institute Theater continues its dual series on screwball comedy and rock. The former offers a double bill of William Wellman's Nothing Sacred and Karel Reisz' mod-flavored British import Morgan! Friday at 9, and again, in reverse order, Sunday at 5. The classic comedy The Thin Man (one of the AFI's consistently biggest draws) shares a bill with Sidney Lumet's Just Tell Me What You Want (Myrna Loy's last screen appearance), Saturday at 5 and Sunday at 8:15.

The rock'n'roll series offers Jayne Mansfield in Frank Tashlin's The Girl Can't Help It Friday at 7 and Saturday at 9. Call 785-4601.

* The MGM Summer Festival at the Circle Theater is showing Elvis Presley's Jailhouse Rock and Mad Dogs and Englishmen, the split-screen stereo extravaganza documenting Joe Cocker's barnstorm tour of America 'way back in 1970. Call 331-7480.

* The Sidwell Cinema, at the school of the same name at 3901 Wisconsin Avenue NW, is showing Jacques Beineix's groundbreaking Diva this weekend. Call 357-8178.

The Washington Film Council and The Production Center at Arthur Young are presenting their fourth summer seminar, Digital Video Effects, Tuesday from 7 to 10 p.m. The speakers will be Production Center senior producer Joan Porter and senior editor John Ullom. Cost is $25 (including refreshments); enrollment is limited. Call Anne Polley at 703/620-4490 for further information. The seminar will be held at the center, 1950 Roland Clarke Place, in Reston.

The Smithsonian's Italian film festival continues Wednesday with the Washington premiere of Nanni Loy's 1984 comedy Where's Picone? starring Giancarlo Giannini. It screens at 8 at Carmichael Auditorium in the American History Building. Tickets are $4 for members of the Smithsonian's Resident Associate Program and $5.50 for the general public. Call 357-3030.

The National Museum of American Art is hosting screenings of With These Hands, an hour-long documentary on American artists/craftsmen on Thursday and again August 22 at 11 a.m., 12:15 and 1:30. Featured artists include Harry Nohr and J.B. Blumk (wood), Peter Voulkos and Paul Soldner (clay), Toshiko Takaez (clay and fiber), Dorian Zachai (fiber), Clayton Bailey (clay, rubber and plastic), and James Tanner (glass). The free screenings will be held in the Grand Salon on the second floor of the Renwick Gallery, 17th and Pennsylvania Avenue NW. Call 357-3095.

According to the Washington-based Motion Picture Information Service, the area's 10 top- grossing pictures for the week ending July 25 were, in descending order, Back to the Future (cruising along with twice the grosses of its nearest competitor, but down to 18 from 19 screens in its third week); Silverado (at 17 houses in week two); E.T. The Extra-Terrestrial (doing swell at 13 locations in the first week of its re-release); Mad Max Beyond Thunderdome (dropping to 21 from 22 screens in week two); Cocoon (still strong at 17 slots in its fifth week); The Man With One Red Shoe (in 15 theaters in its debut); St. Elmo's Fire (moving from 14 to 13 screens in a full month of release); George A. Romero's Day of the Dead (12 locations in its first week); Rambo: First Blood Part II (dropping three screens to 14 in week nine); and Pale Rider (moving from 20 to 19 houses in week four).

THE PAGES OF FILM HISTORY -- Myrna Loy, Gary Merrill, Beatrice Straight (winner of Best Supporting Actress Oscar in "Network"), author James Baldwin, Carroll O'Connor and Peter O'Toole are among those marking birthdays Friday. This date also marks the birth of Pierre Charles L'Enfant (who designed, among other things, Washington's nifty traffic circles).

Happy birthday Saturday to Tony Bennett, Ramon Estevez (better known as Martin Sheen) and Jay North (TV's "Dennis the Menace").

CORRECTION -- Last week's column incorrectly referred to former actor Darryl Hickman as "Dobie Gillis himself." His younger brother Dwayne played Dobie Gillis.