And then there are those days you can't abide the thought of sitting for hours on that highway- become-parking-lot, U.S. 50. You might be shackled to your beeper, or perhaps it's tots'n'teens day at the community pool. Well, don't let that stop you from catching some rays. A beach is a state of mind; just ask Interior Secretary Watt.

The most obvious in-town beach is the Mall. Some Sundays it resembles Woodstock on the third day, with tourists stepping over trunk-clad tanners strewn from Monu ment to Capitol. When the heat gets too intense, just dive into a cool museum or two. And while parents bask, kids can play ball, throw Frisbees or climb up on old Uncle Beasley, the triceratops that welcomes visitors to the Museum of Natural History.

Need real water to enhance the fantasy? One of the prettiest Potomac-view parks is Lady Bird Johnson, the one just over the 14th Street Bridge with the teensy parking lot and the not- so-teensy gull statue. Most of the people who frequent this place are smart enough to go by bicycle, and the whole area is clean and green and stirring with breezes off the river.

Hains Point is another grass beach with a fine view of the Potomac, the Anacostia and Washington Channel. Sun bathing here seems to be a family affair, and lots of folks bring picnics and pets.

Belle Haven is also a beach with a family- tanning atmosphere. Between Alexandria and Mount Vernon on the George Washington Parkway, it features plenty of parking, picnic tables, grills and a nice Potomac panorama.

Less serene but plenty sunny is Watergate Beach on Rock Creek Parkway near Virginia Avenue. This place is hardly Washington's best- kept secret; on a balmy Saturday you're likely to bump elbows with the person lying next to you, which isn't such a bad way to meet people.

For quiet beauty, there's Constitution Gardens, between the Washington Monument and the Reflecting Pool. There's plenty of shade for the half-hearted bather, what with the azaleas and maples surrounding the large pond.

If a fountain will suffice as imaginary oceanfront, and you think serene is for libraries, try Dupont Circle. There's usually a sampling from every age and persuasion there, and it's a common gathering spot for street artists and musicians. Talk about your good vibrations.

P Street Beach -- bordering Rock Creek Parkway, between Dupont Circle and Georgetown -- is bigger, better-known and a bit more specialized. Bronze bods are serious biz on this urban beach, particularly for the mostly male crowd that frequents it. Definitely not the place to go looking for maillots.

Finally, for the family that sun-worships together, Lincoln Park at 11th Street and East Capitol is a verdantly wholesome spot. Serious bathers tend to gather at the west side, but there's a tot lot on the opposite end and lots of space for picnicking in between. Just keep a keen eye for the occasional canine memento, and you'll find plenty of space to spread out a beach towel.