A cappella "heavy mental" music trio Betty performs two shows of their original tunes (and distinctive Bettychatter) at Lisner Auditorium, 21st and H NW, at 8 Friday and Saturday. Proceeds ($15 at the door) will help send Betty to Moscow for an artists' exchange program. 994-6800.


Mums are the word at the Brookside Gardens Chrysanthemum show 9 to 5 daily till November 29 at 1500 Glenallan Ave. in Wheaton. 949-8231 . . . the Montgomery County Antique Glass Show and sale is 11 to 9 Saturday and 11 to 6 Sunday at Armory Place, Wayne and Fenton streets in Silver Spring. $3. 589-9581 . . . Flamenco dancer Marina Keet and the Spanish Dance Society perform at Bloomingdale's at White Flint between 1 and 2 and at the Tysons Corner store between 2 and 3 both on Saturday. Free. 393-3600 . . . the Smithsonian's Palm Court Cameos continue at the National Museum of American History (12th and Constitution NW) with vocal performances of Irving Berlin music at noon Friday and at 1:30 and 3:30 Sunday. Free. 357-2700 . . . The Northern Virginia Model Railroaders open house is 1 to 5 Saturday and Sunday at the Washington and Old Dominion Railroad Station, Dominion and Ayr roads in Vienna. Free. 938-5157.


Chapters Bookstore is where Ratty, Badger, Mole and Mr. Toad will be to bring alive excerpts of the children's tale "The Wind in the Willows." The characters are actually part of Glen Echo's Adventure Theater and their free performance begins at noon Saturday at the bookstore, 1613 I St. NW. 861-1333.


The 39th annual bazaar at St. Mary's Armenian Apostolic Church, 42nd and Fessenden streets NW, offers Armenian delicacies, shish kebab dinners and an Oriental rug sale 11 to 2 and 6 to 9 Friday and 12 to 3 and 6 to 9 Saturday. Free. 363-1923.

The Aki-No-Ichi Japanese fall festival is 11 to 4 Sunday at Walt Whitman High School, 7100 Whittier Blvd. in Bethesda. Besides such foods as beef teriyaki, sushi and noodles, there'll be crafts, Minyo folk dancing, Jujitsu self-defense and a calligraphy exhibit. 845-0099.

For a little bit of Eastern Europe, check out the Polish Bazaar 11 to 5 Saturday at American Legion Hall, 9218 Baltimore Ave. in College Park. After a stop at the Polish deli and bakery, dance to live polka music and see the dancing Polka Belles and Beaus. 262-2441.


The Singing Capital Chorus will have the weekend in tune with their 41st annual fall show "Broadway in Barbershop" in Constitution Hall at 8 Saturday. The program includes showtunes by Al Jolson and George M. Cohan, among others. Tickets are $6 to $10 and available at the door. 966-8788.


American Deborah Shapiro and Swede Rolf Bjelke began their two-year trek in 1982 -- the first Arctic to Antarctic private sailing voyage. Along the way they took more than 14,000 pictures and recorded dozens of tapes. This weekend the couple will present these images and sounds in a two-hour audio- visual show at 8 Saturday at the Maryland Hall for the Creative Arts (on Greenfield Street near West Street in Annapolis) and at 8 Sunday at Georgetown University's Gaston Hall. It's $10 at the door. 301/539-2665.


Veterans Day being next week, the U.S Army Band performs at 8 Saturday at the Patriot Center in a "Bicentennial Salute to Veterans." Tickets are free but required; get them at Building 32 at Fort McNair (Fourth and P SW) or by calling 475-0685.


The 12th annual Marine Corps Marathon, the fourth largest race in the country, brings more than 11,600 runners to town beginning at 9:05 a.m. Sunday. Runners -- including two-time winner Brad Ingram, 75-year-old George Capraru of Canada and 5-month-old Eleanor Petropulos (who'll catch a ride on her Dad, Larry) of Virginia -- will begin at the Marine Corps War Memorial (Iwo Jima), traverse Key Bridge and M Street, hitting Rock Creek Park, Constitution Avenue, the Capitol and Hains Point, with a finish back near the Iwo Jima. (There's a map and details in Friday's Sports section.) Call 521-1900 for more information.


The fifth annual Head of the Occoquan Rowing Regatta is 11 to 4 Saturday with more than 20 races, including men's and women's recreational singles, collegiate championship eights, as well as clubs, elite and masters teams. Spectating is free at Sandy Run Regional Park. (Take I-95 south to the Lorton exit to Lorton Road, bear right on Ox Road, left at the sign for Fountainhead Regional Park and follow signs for Van Thompson Road and the races.) Call 223-8232.


The Arlington Craft Guild's fourth annual holiday sale is 10 to 6 Friday, 10 to 5 Saturday and 10 to 4 Sunday at the Overlee Community Association's Club House, 6030 Lee Highway in Arlington. This juried show by 12 artists includes baskets, pottery, batik and more. Free. 241-9286.

More arts and crafts can be found at the "Handcrafted Christmas From Lancaster, Pennsylvania" show at the Women's Club of Falls Church, (222 North Washington St.), where you can peruse the one-of-a-kind folk art of 35 artists, including stained glass, dolls and furnishings 6 to 9 Friday, 8:30 to 6:30 Saturday and noon to 5 Sunday. It's $2.50; free for under 12. 241-9281.


The Prince George's Civic Opera puts opera in its witty place with a production of Lehar's "The Merry Widow." Showtimes are at 8 Friday and 3 Sunday at Queen Anne Fine Arts Auditorium at the Prince George's Community College, 301 Largo Rd., Largo (near the Capital Centre). Tickets are $10 and $15, at the door. 829-8802.