Tennis Everyone? Tennis treats abound as the Rock Creek Tennis Stadium (16th and Kennedy streets NW) plays host to two professional tournaments that run concurrently this weekend. General admission tickets for both Saturday and Sunday are $8 and allow you to watch all the action on the stadium's five courts.

*Though the likes of Yannick Noah (who's injured, yet still scheduled to play as of this writing), Guillermo Vilas and Andres Gomez won't toe the baseline until next week, you can still see 56 dark horses vie in qualifying rounds of the Sovran Bank/D.C. National Tennis Classic this Saturday beginning at 10:30; Sunday at 11. The August 3 finals are sold out, but a limited number of tickets remain available for the semifinals (August 2, $18) and the quarter-finals (August 1, $15). For more information, call 429-0690 or 432-0200.

*Aging tennis stars don't fade away, they become "grand champions." You can see that the old men (35 and up) still swat a mean ball during the Prudential-Bache Securities Grand Champions Tournament. Players include the 1986 Wimbledon Men's 35-and-over champion, Jaime Fillol, along with Stan Smith, Manuel Orantes, Cliff Richey and Dick Stockton. The finals are Monday at 7. Tickets for that are $8 and $9. 429-0690 or 432-0200.

*And while you're at it, you can check out the Third Annual Wheelchair Tennis Tournament, which is Saturday from 9 to 6; Sunday from 9 to 2 on the courts outside Rock Creek Stadium. Free. 649-3950. Hoopla

You can see the stars of tomorrow this weekend when the final eight out of 38 teams from around the nation compete in the AAU 17-and-Under National Basketball Championship at Georgetown University's McDonough Arena. The quarterfinals are Friday beginning at 9 a.m. The semis are that evening at 6:30 and 8. The championship game is Saturday at 1 (consolation games begin at 10). Tickets ($3 for adults, $2 for 17 and under) are available at the door. 944-3300. (For a further look at this and 14 other AAU. competitions this weekend, see page 53.) Making Their Mark

If you've been dying to meet a walking-talking bottle of Heinz ketchup, Tony the Tiger, the Michelin Man or even the Campbell Soup twins, your day has arrived. They'll all be working overtime at the United States Patent and Trademark Office's Fourth Annual National Trademark Exposition, which is Saturday and Sunday from 9 to 5 in the Great Hall of the U.S. Department of Commerce on Pennsylvania Avenue NW (between 14th and 15th streets NW). Eighteen exhibitors tell you about the genesis of their famous trademarks and give away samples of their products. Admission is free. By Metrorail exit at the Federal Triangle station on the Blue/Orange lines. 557-3341 or 789-7012. Music Mania

Look here, there's something for every ear:

*Living legends Fats Domino and the Killer himself, Jerry Lee Lewis, team up for a concert of classic rock 'n' roll at George Mason University's Patriot Center Friday at 8. Tickets, $15.50, are available at the door and area ticket outlets. The university is at 4400 Fairfax Drive in Fairfax. 432-0200 or 703/323-2672.

*For country fans, Sunday's Eighth Annual Bull Run Jamboree offers Lee Greenwood, Reba McEntire, the Forester Sisters and Mel McDaniel. The Country Bach Band kicks it all off beginning at 10 a.m. (gates open at 6). You can also take part in such contests as corn-on-the-cob eating, log-sawing and hay-bale throwing (from 10 to noon). Advance tickets, $12, are available at Fotomat outlets and Northern Virginia Regional Park offices. Admission at the gate is $14. To get to Bull Run Regional Park, take the Centreville Exit off I-66 and follow signs. 352-5908 or 631-0550. (For a review of the latest records by Greenwood, McEntire and the Forester Sisters, see page 15.)

*Wolf Trap has a corner on the classical music scene with the National Symphony Orchestra playing two concerts. Hugh Wolff conducts the "1812 Overture" (cannons and all) in an all-Tchaikovsky program Friday at 8:30. Then at 8:30 Saturday, the NSO bids farewell to associate conductor Andrew Litton, who leads a concert of music by Gershwin and Ravel. Litton -- who'll be moving to England, to be principal guest conductor of the Bournemouth Symphony Orchestra -- also gives a lecture and demonstration on Gershwin at 1 on Saturday. Cost for that is $5. Both the lecture and the concerts are in the Filene Center. Tickets for the concerts, $10 to $20, are available at the door or at 385-0044.

Wolf Trap also has something for folk fans -- a concert by Peter, Paul and Mary Sunday at 8. Tickets, $10 to $20, are available at the door or at 385-0044.

*The Care Free Curl Summerfest hits Washington with a funk and r&b concert featuring Morris Day, Jermaine Jackson, Midnight Star, Ready for the World and The Jetts. It's Friday at 8 at the Capital Centre. Tickets, $16.50, are available at area outlets and the door. 350-3400 or 432-0200. (A review of Midnight Star's newest release appears on page 15. Rest of the Best IN TOWN

Chilean journalist and poet Ariel Dorfman reads from his work and discusses the relationship between Latin American culture and politics Friday at 8 at St. Margaret's Church, 1820 Connecticut Avenue NW. Tickets, $2, are available at the door on a first-come basis . . . The free Concerts on the Canal series continues Sunday from 1:30 to 4:30 with music from the Chesterbrooke String Quartet and the Trinidad and Tobago Steel Band. The concert's on the C&O Canal (Thomas Jefferson and 30th streets in Georgetown). 965-3100. IN VIRGINIA

The McLean Jazz Workshop plays tunes by Duke Ellington, Count Basie, Glenn Miller and Benny Goodman Friday at 8 in the the McLean Community Center's Alden Theater, 1234 Ingleside Avenue in McLean. Tickets ($5, $4 for students and seniors) are available at the door (beginning at 7) or by calling 790-9248.