The swearing-in of the president may be the centerpiece of the inaugural activities, but there's plenty going on all around this weekend. Here are some of the highlights. All are open to the public and, unless otherwise noted, are free. FRIDAY

11 A.M. TO 9 P.M. -- Continuous concerts at the National Air and Space Museum and the National Museum of American History, featuring American popular song, jazz, ragtime, chamber music, gospel, traditional ethnic music, big band, square dancing and country music. For specific scheduling information, see list on page 7.

NOON TO 8 P.M. -- The Pavilion at the Old Post Office presents almost continuous entertainment featuring music from around the country performed by artists from various states.

NOON TO 4 P.M. -- "A Taste of America," with foods from fifty restaurants, at the Washington Convention Center. Tickets, at $9.50, are available through Ticketron and at the "will call" pick-up station at the Convention Center.

6 P.M. -- Concert at the Netherlands Carillon adjacent to the Iwo Jima Memorial in Arlington. Bell tower will be open to the public during the concert and remain open for those who want to view the fireworks on the Ellipse.

6 TO 7:15 P.M. -- Inaugural prelude pageant, with military bands, actor Fess Parker, 250 dancers and President Reagan and Vice President Bush. Fireworks follow. On the Ellipse.

8 P.M. -- The National Theater presents the Army's Soldier Show, a musical revue entitled "All You Can Be and More." Call 783-3370 for free tickets. SATURDAY

10 A.M., 3 AND 8 P.M. -- The National Theater repeats its presentation of "All You Can Be and More." Call 783-3370 for free tickets.

10 A.M. TO 3 P.M. -- Shw of political memorabilia, Marvin Center, George Washington University. Bring your old campaign paraphernalia for free appraisals. For more information, call 955-6667 or 556-8108.

11 A.M. TO 9 P.M. -- Continuous concerts at the National Air and Space Museum and the National Museum of American History. For details, see list on page 7.

11 A.M. TO 9 P.M. -- The Pavilion at the Old Post Office continues its offering of music from around the country.

NOON TO 4 P.M. -- "A Taste of America" at the Washington Convention Center. See Friday's listing. SUNDAY

11 A.M. TO 9 P.M. -- Continuous concerts at the National Air and Space Museum and the National Museum of American History. See details on page 7.

NOON UNTIL 3 P.M. -- Concerts by inaugural parade bands in Western Plaza.

1 TO 5 P.M. -- "A Taste of America' at Washington Convention Center. See Friday's listing.

5:30 TO 7 P.M. -- Patriotic songs by choral groups from schools across the country, at the Jefferson Memorial. Fireworks follow. MONDAY

10 A.M. -- Concert at the Taft Memorial Carillon on the Capitol Grounds, by Edward M. Nassor, carillonneur.

11 A.M. TO 9 P.M. -- The Pavilion at the Old Post Office continues its musical tribute to the states before and after the Inaugural parade.

11:30 A.M. -- The official inaugural ceremony at the Capitol. If you don't have tickets, there will be a first-come first-served viewing area around the Grant Memorial. The speeches will be carried by loudspeaker. BYO portable television.

NOON TO 9 P.M. -- Continuous concerts at the Smithsonian's National Museum of American History. See details on page 7.

2 P.M. -- The Inaugural parade.

7 AND 8:30 P.M. -- The Victorian Lyric Opera presents Gilbert and Sullivan's "Iolanthe" at the National Theater. For free tickets, call 783- 3370.