SUMMERTIME, and the livin' is easy.

So's the music, which abounds like salmon in season. And much of what's offered is done so under the stars, or, for a few dollars more, under a roof with the walls rolled down (in case you don't want to spend a fortune on moonscreen).

There are three major summer venues in Washington: the Carter Barron Amphitheater at 16th and Colorado; the Merriweather Post Pavilion in Columbia, Md.; and Wolf Trap in Vienna. These sites will serve up three quarters of the pop concerts, though RFK Stadium will be offering the biggest blowouts of the season.

For instance, there's Saturday's Go-Go extravaganza, featuring many of Washington's finest, including Rare Essence, EU, Sweet Cookie, Big Tony and the Trouble Crew, Little Benny and the Masters, Scorpio and Hot Cold Sweat (New York's Heavy D and the Boyz and Kool Moe Dee bring a little rap essence to the bill). A week later, it's the Budweiser Superfest with Luther Vandross, Patti LaBelle, Maze and Frankie Beverly, Gladys Knight and the Pips, the Gap Band and Atlantic Starr.

OK, so maybe-it's-her-last-tour-so-be-there-or-be-square: Madonna and Club Nouveau turn the heat up July 2 (just what we'll be needing, undoubtedly) at RFK. Two days later, on the 4th, it's the all-star Welcome Home concert with the likes of Neil Diamond, Crosby, Stills and Nash, James Brown, Anita Baker, George Carlin, John Fogerty, the Four Tops, Ben E. King, Kris Kristofferson, Linda Ronstadt and others. It starts at 1:30 p.m., and HBO will delay-cablecast it that night. (The musical emphasis on the Mall this national holiday: classical in the form of the NSO at the Capitol, and military bands around the Sylvan.)

On September 5 at RFK, it's the all-star Greenpeace concert, a Live-Aid style television event being held in tandem with an all-star Moscow concert. The only confirmed act so far is Boston, but it's rumored that some big names are scheduled for both locations; the feed will go round the world.

And yes, Bull Run Park in Centreville will be having its annual country music festival on August 2, with the Judds, Sawyer Brown, Ronnie McDowell, Pake McEntire and Pinkerton and Bowden. Bluegrass fans will note that festivals, usually of the weekend variety, can be found several times a month within a reasonable driving distance of the nation's capital.

If the stars come out in clusters at RFK, elsewhere they tend to come individually. At the Post Pavilion, the trend this year is to fewer acts, but with longer stands: Jimmy Buffett (June 27 & 28); Neil Diamond (July 3 & 4); Whitney Houston (July 11 & 12); Heart (July 17 & 18); The Monkees (August 6 & 7); Anita Baker (August 15, 16 & 17) and Tina Turner (August 22 & 23).

Other hot Pavilion shows include Paul Simon and his "Graceland" show (July 1); Crosby, Stills & Nash, and maybe even Young (July 6) ; the return of Dan Fogelberg (July 25); and Al Jarreau and Chaka Khan (August 5).

Over at Wolf Trap, it's a star-filled tribute to jazz legend and innovator Dizzy Gillespie Saturday. Some three dozen of the trumpeter's friends, fellow musicians and admirers (including Wynton Marsalis, Sonny Rollins and Benny Carter) will celebrate half a century of Gillespiana in what promises to be the jazz event of the year.

Promising concerts include Tony Bennett with the Count Basie Orchestra (next Wednesday); the return of Blood, Sweat and Tears with original vocalist David Clayton-Thomas (July 1); James Galway and the Chieftains (July 16); James Brown and Perry Como (no, they're separate shows, July 17 and 19 respectively); Burt Bacharach and Dionne Warwick, together again (July 22); the Michael Franks, Stanley Jordan, Bobby McFerrin triple bill on August 5 and red-hot-bluesman Robert Cray (August 25).

The emphasis at the Carter Barron, at 39 the granddaddy of Washington's summer venues, is on R&B, soul, funk and jazz, with shows every Saturday and Sunday. If you like expressive singers, you might want to check out the camping facilities (just kidding, though with $8.50 tickets for all shows, this is the least expensive way to enjoy live music that isn't entirely free, like the weekend jazz shows at Fort Dupont, or the Wednesday big band concerts at the Sylvan Theater).

Highlights at the Carter Barron: Nancy Wilson and local man making good Carl Anderson (June 20); Roberta Flack (June 28); the O'Jays (July 11 & 12); Jennifer Holiday (July 25), Ray, Goodman and Brown with Najee and Sarah Dash (August 15); and Oran "Juice" Jones and Shirley Murdock (August 29). The season ends with a salsa party featuring Willie Colon and Eddie Palmieri (August 30).

There are free concert series scheduled at the C&O Canal, the Lubber Run Amphitheater in Arlington, and elsewhere (study those Weekend listings every week). This Saturday and Sunday, Glen Echo is the site of the annual and still free Washington Folk Festival, which uncovers and celebrates the rich, multi-ethnic and polycultural mix that makes Washington such an interesting place to eat and/or catch a cab.

Speaking of folk festivals, the annual Festival of American Folklife will be held on the Mall June 24 to 28 and July 1 to 5 and Washington performers will be the focus of the music stage programs. Also highlighted: the culture, music, crafts, food and occupational traditions of Michigan and something called "Cultural Conservation and Language: America's Many Voices." Don't worry, it's always much more interesting than it sounds. And it's still free, too.