See the cutting edge of the two-wheeled world, including the six-cylinder Honda Gold Wing and the BMW paralever- suspension R100GS, at the Great American Motorcycle Show at the D.C. Convention Center (Ninth and L NW) 5 to 10 Friday, 10 to 10 Saturday and 10 to 6 Sunday where more than 200 bikes will be displayed and folks from BMW, Harley-Davidson, Honda, Kawasaki, Yamaha and Suzuki will be around to answer questions. It's $6; $3 for kids 6 to 11. 371-4200. BLAST FROM THE PAST

In-A-Gadda-Da-Vida? On-A-Pennsylvania-Avenue? Yes: The original Iron Butterfly performs on their first tour in 18 years at 9:30 Saturday at the Old Post Office Pavilion, with opening band the Roadducks. It's $7.50 at the door; advance tickets are available at the Have-A-Heart novelty store (in the Pavilion) or at any Providence Savings and Loan. Proceeds benefit Children's Hospital. Call co-sponsors WCXR-FM at 683-3000. LEAPS AND BOUNDS

The Choreographers' Showcase brings the work of eight area choreographers to the Publick Playhouse, 5445 Landover Rd. in Hyattsville at 8 Friday, including Meriam Rosen, Buffy Price and Alvin Mayes, among others. Tickets are $8; $6 for students and seniors. (See Pamela Sommers' preview on page 13.) Call 277-1710. FREE CRAB

The Annapolis trio Crab Alley will be singing and strumming original songs about the Chesapeake at 9:30 and again at 11 Saturday morning at the National Theatre. With ukulele and guitar, Crab Alley performs songs about the area's wayfaring watermen and wildlife. The family program is free; seating's on a first-come, first-served basis. Call 783-3372. PASSING NOTES

Many free concerts to choose from this weekend: Cellist Rafael Figueroa and pianist Wu Han perform in the Coolidge Auditorium of the Library of Congress at 5:30 Saturday. 287-5502 . . . also in the Coolidge auditorium, there'll be a Marine Band chamber recital at 3 Sunday with polka, rumba, cake walk and other dance music. 433-4011 . . . the 20 members of the Continuum Chamber Singers perform a program of "The Sacred and the Profane" music of the 15th and 16th centuries at 3 Saturday at the Anderson House Museum, 2118 Massachusetts Ave. NW. 785-0540 . . . the Washington Conservatory Orchestra performs with Ricardo Cyncynates, assistant principal violinist of the NSO, and NSO affiliate conductor Fabio Mechetti at 4 Sunday at La Maison Francaise, 4101 Reservoir Rd. NW. Call 320-2770. REST OF THE BEST

The Maryland Antiques Show and Sale is at the Baltimore Convention Center noon to 9 Friday and Saturday and noon to 6 Sunday; $5 per day. 301/685-3750 . . . The sixth annual Seaside Boat Show is 4 to 9 Friday, 10 to 9 Saturday and 10 to 6 Sunday at the Ocean City Convention Center (40th and Coastal Highway); $3.75. 301/524-9000 . . . the Lots-a-Luck Bassmasters hold a bass fishing show 10 to 5 Sunday at the Tysons Westpark Hotel, Tysons Corner in McLean. It's $4. 430-4137 or 734-2800 . . . The West Mexican music of Mariachi Los Amigos includes violins, trumpets, guitarron, vihuela and singing -- all at the WES Auditorium, 7750 16th St. NW (at Kalmia Road) at 8:30 Friday, under the auspices of the Folklore Society of Greater Washington. Tickets are $4. 281-2228 . . . the free U.S. Air Force Band's Guest Artist Series continues at 3 Sunday with choral director Roger Wagner conducting the Singing Sergeants and Navy Sea Chanters at DAR Constitution Hall. 767-5658. A LA DOGUE

The clothes horses are all dogs at this weekend's "Have a Heart Doggie Fashion Show" benefit noon to 2 Sunday at the Biograph Theater (2819 M St. NW in Georgetown). Emceed by columnist Karen Feld and her pooch Champagne, the show (doggie evening gowns, sportswear and swimwear included) will be followed by a tea (with dog biscuits) and Humane Society dog movies. Tickets are $10; $5 for kids under 13. Proceeds benefit the Washington Humane Society. Call 333-8349. SWEET TREAT

The romantic strains of the 12-man Chanticleer vocal ensemble fill the Baird Auditorium of the Smithsonian's National Museum of Natural History at 3:30 Sunday, Valentine's Day. In their Washington debut, the a cappella group will perform the sweeter works of Josquin des Prez, Cole Porter and Stephen Sondheim, among others. Tickets are $12. Call 357-3030.

Meanwhile, the Concord Chamber Ensemble performs a free Valentine's Day concert of instrumental and vocal chamber music from Great Britain. It's at 3 Sunday at the Art Barn, 2401 Tilden St. NW. Call 565-0951. GET CENTERED

At the eighth annual "Heart to Heart Festival: The Quest for Inner Peace," you can sample the newest of New Age philosophies and activities via work- shops, talks, exhibits and demon- strations. Besides workshops in free-form dancing, natural healing, crystals and psychic readings, featured speakers include actor Dennis Weaver, Yogi Bhajan (founder of the 3HO Foundation) and medicine chief Sun Bear. It's 8:30 to 7 Saturday (followed by a dance till 9) and 8:30 to 5:30 Sunday; $20 for both days, $12 for one day at the Departmental Auditorium on Constitution between 12th and 14th NW. 986-1223.