Baltimore has a lot more going for it this weekend than just the slugging Orioles. The big spring fling is the HOPKINS SPRING FAIR, and annual event on the Johns Hopkins University campus (Charles and 34th Streets). Besides arts-and-crafts exhibitions and ethnic-food stands, there are magic shows and pony rides for kids, and continuous musical performances on two outdoor stages. Other highlights include a lacrosse game Saturday (national champs Hopkins play Army) at 2, comedian Kelly Monteith at 7 and 10:30, and, Sunday at 7:30, Tom Taylor doing the Woody Guthrie show he did recently at Ford's. Admission to the fair is free and hours are: Friday, noon to 6; Saturday and Sunday, 10 to 6.

WHAT'S WHERE

You can get your bearings in Baltimore in several ways. First, get a map and brochures at the OFFICE OF PROMOTION AND TOURISM, 110 West Baltimore Street. Saturday and Sunday, 11 to 4. 301/685-8689.

If you want to play it safe, there are several organized ways to see the city. The BALTIMORE TOUR BUS, leaving from the Inner Harbor at 10, is a 3 1/2-hour introduction to historic sites and oddities. 301/752-8637. Have car, will tour: you can also rent TOURTAPES OF BALTIMORE, complete with player, at the Hilton Hotel (Fayette and Liberty Streets), the Office of Tourism or Maryland Science Center (Light Street and Key Highway). Tours focus either on "Historic Baltimore" or " Cultural and Religious Baltimore." 301/486-8989. For a more luxurious glimpse, how about a limo tour? For $100, a RENT-A-TOUR guide will tailor a tour to your interests. 301/653-2998.

As you survey the sites, two buildings will stand above the rest. The one that might remind you of the East Wing of the National Gallery is the WORLD TRADE CENTER, the tallest building in the city, and was designed by I.M. Pei, also the East Wing's architect. The older building with the huge clock now houses administrative offices of the Maryland Arts Council and was built in 1911 to copy the Palazzo Vecchio in Florence. Look at the clock carefully: Instead of numbers, time is marked with the letters "B-R-O-M-O-S-E-L-T-Z-E-R."

WANDERING

Meandering around can be especially satisfying in a city that prides itself on its neighborhood life. Federal Hill, overlooking the harbor, was named in the celebrations following the ratification of the Constitution. During the Civil War, the Union stationed cannons there, pointing at the heart of the city, to make sure Baltimore remembered which side it was on. From there, walk to the Inner Harbor, a much-touted renovation project, and see the MARYLAND SCIENCE CENTER, 601 Light Street, a please-touch science museum, open 10 to 10 Friday and Saturday and noon to 6 Sunday. 301/685-5225. On the other side of the Harbor, you'll see the U.S.S. CONSTELLATION. The ship won't be open until May 1, but you're getting a glimpse of the birthplace of the "Star-Spangled Banner," for Francis Scott Key composed our national anthem from its decks - looking at FORT McHENRY, which is also in Baltimore.

Another area ripe for exploring is ANTIQUE ROW, a solid string of shops on the 800 block of North Howard Street. Behind it are boutiques and many renovated homes along quiet side streets.

MUSEUMS

The most famous and on e of the best-loved Baltimore exhibits is the Cone Collection at the BALTIMORE MUSEUM OF ART, the private collection of the Cone sisters, who were friends with Gertrude Stein (she studied at Johns Hopkins) and were greatly influenced by her artistic tastes, especially in Henri Matisse. It's free and just south of Johns Hopkins on Art Museum Drive, and hours are 11 to 5 Tuesday through Saturday and 1 to 5 Sunday. 301/396-7100.

The WALTERS ART GALLERY, 600 North Charles Street, is another fine museum, now showing "Treasures in Cyprus." Best yet, the museum is located in Mount Vernon Square with its cobblestones, small parks, old churches and a monument to George Washington. Admission is free; 1 to 5 Monday, 11 to 5 Tuesday through Saturday and 2 to 5 Sunday. 301/547-9000. Of the many other, smaller museums with specialized collections, the BABE RUTH HOUSE, 216 Emory Street, will surely appeal to baseball buffs. The birthplace of the "Sultan of Swat" is filled with memorabilia, including his uniforms. Open 10:30 to 4 Wednesday through Sunday. 301/752-1539.

A SMATTERING OF THEATER

Local theater-goers enjoy CENTER STAGE, 700 North Calvert Street, which has reasonably priced tickets, a pleasant bar for a pre- or post-show drink and, most importantly, good acoustics."Measure for Measure" is on now. 301/332-0033. Other fare ranges from "Grease" at the MORRIS MECHANIC, Hopkins Plaza (301/727-4103), to such experimental spots as THEATRE PROJECT, 45 West Preston Street. This weekend, "Mixed Company," a group from Toronto, performs two short plays, one of which is described as a "wacky dialogue between Noah and God." Free, donations accepted. 301/539-3090.

VIBES AND NIGHTLIFE

But then, you might prefer music. The classical highlight of the weekend is at the classical highlight of the weekend is at the PEABODY CONSERVATORY (near the Walters Art Gallery), a well-known music school. Friday and Saturday nights at 8:15 the students will perform two operas, Ravel's "L'Enfant et les Sortileges" and Puccini's "Il Tavarro." 301/837-0600.

One good bet for jazz is the FAMOUS BALLROOM, 1717 North Charles Street, a seedy Baltimore institution that has shows on Sunday evenings, 5 to 9. BYOB to listen to the great and will-be-great. 301/945-2266. Another place, recently opened but already popular, is the BANDSTAND, 616-20 Fleet Street. Roy Brooks and Marcus Belgrave perform this weekend in the small club. If you go to the Bandstand, you'll be in FELL'S POINT, an area down by the water once reserved for sailors and wandering writers like John Dos Passos. Now there are saloons for weekending suburbanites, local characters and, yes, even sailors. Sunday, take in a poetry reading with your beer: prize-winning poet David Bergman reads at 7:30 at the ANGEL, 1812 Bank Street, as part of a program of weekly readings at area bars.

A FINAL WORD

The usual disclaimer: There's a whole lot more to Baltimore than appears above, and, since it's only an hour away, you might want to take a few visits to sample it all. CAPTION: Picture, NOT ALL OF BALTIMORE'S HOUSES HAVE WHITE MARBLE STEPS. By Charles Del Vecchio