At mid-summer, most people have a pretty good idea of their vacation plans. But if you don't, here are some last-minute possibilities for a quick and convenient getaway between now and Labor Day:

*Go to the beach: Most of the beach-view houses and apartments on the nearby Delaware and Maryland coasts are snapped up early. But even this late in the season you can usually find a place to rent for a week or two within easy walking distance of the ocean.

In Rehoboth Beach, Del., one of the most popular Atlantic resort towns, Alma Ashley, rental manager for the Anderson-Stokes reservation service, expects to have a variety of accommodations available for the rest of the summer, some of them on "the ocean block." By that she means you don't have to cross any streets to reach the beach.

As of this month, she was still offering ocean-block efficiency apartments in August for two people at $455 a week, from Saturday check-in at 2 p.m. to Saturday check-out a week later at 10 a.m. About 10 blocks from the beach, eight-person townhouses were available for $550 a week. Closer to the beach, the rental rate for an eight-person townhouse jumps to between $900 and $1,400 a week. All are cleaned and ready for occupancy when you arrive.

Each beach community -- Lewes, Rehoboth Beach, Bethany Beach and Fenwick Island in Delaware and Ocean City, Md. -- is served by one or more reservation services. Check with the local chamber of commerce for a list of their names.

For more information: Anderson-Stokes Leisure Reservations Inc., Rehoboth Beach office, (302) 227-3821.

*Escape to New England: Smugglers' Notch, in the mountainous northern tip of Vermont, is an all-season resort that goes out of its way to welcome vacationing families. It devotes a great deal of attention to the youngsters and keeps costs at a reasonable level for family budgets.

A resort village surrounded by ski terrain, Smugglers' Notch is offering a seven-day "Familyfest" package this summer for two adults and up to four children for $599 to $699. Accommodations are in a condominium apartment, and the rate includes unlimited tennis and swimming in the resort pool; a Sunday champagne or soda brunch; an old-fashioned barbecue dinner one night (chicken, ribs, corn on the cob, salads); an hour's session in the Spa (exercise room, sauna, hot tub); and a New England hayride.

Additionally, children ages 6 to 12 are welcomed at no extra charge into the resort's Discovery Day Camp. The camp operates throughout the day, and youngsters can drop in and out at any time. Programs feature daily tennis and swimming lessons and special supervised outings that may include river-tubing on one afternoon and an overnight hike and camp-out.

Other activities for adults and children: hiking, bicycling, tennis, balloon rides and golf at the 18-hole course in nearby Stowe, a traditional New England village of white-shingled buildings and steepled churches. Day-long van tours are arranged each week for sightseeing trips to Montreal and rambles through the Vermont countryside.

For information and reservations: The Village at Smugglers' Notch, Smugglers' Notch, Vt. 05464, (802) 644-8851.

*Explore the Rockies: Skiers know Copper Mountain as one of the premier ski resorts of the Colorado Rockies. Well, the resort doesn't shut down when the snow melts and the skiers go home. Summer in the Rockies is gorgeous, and Copper Mountain makes the most of it.

This resort also is a self-contained village of hotels, condominium apartments and 35 shops and restaurants, about 70 miles west of Denver (via I-70) in the Arapaho National Forest. The pine-covered ski mountain rises directly behind the village, and a small lake and 18-hole golf course fill the valley in front.

The resort is ideally situated for touring the mountain countryside, including the former mining towns of Breckenridge (a ski resort itself) and Central City, where you can explore a mine or watch a summer opera production in the historic opera house.

A full day's outing takes you across Trail Ridge Road in Rocky Mountain National Park, the highest through highway in the United States. The route crests at 12,183 feet, well above the treeline in a rock and tundra-like landscape. The views are magnificent.

Back at the village, Copper Mountain offers a seven-day summer package for four adults (that is, two parents and two children 12 and older) for $240 per person. (There is no charge for children under 12.) Accommodations are in a hotel or a condominium apartment, and the rate includes a choice of a half-day's white-water raft trip or a four-wheel-drive excursion over high mountain back roads; use of the indoor pool, tennis courts and racquetball courts; and aerobics classes.

Also available: hiking, fishing, a 40-mile paved bicycle trail along Ten Mile Creek, horseback riding, and windsurfing and sailing on Lake Dillon, about seven miles away. Plenty of activities, but the scenery alone is worth the trip.

For information and reservations: Copper Mountain Resort, P.O. Box 3001, Copper Mountain, Colo. 80443, (800) 525-3878.

*Relax in the Caribbean: Winter is the "in" season in the Caribbean, but in the summer, the crowds disappear and hotel prices drop. The sun and the sea, the big attractions of an island holiday, remain inviting year-round.

In the U.S. Virgin Islands, for example, hotels cut their rates as much as 40 percent, says Jose' Vazquez, manager of the Virgin Islands' tourism office in Washington. Travelers should have no trouble finding good beach accommodations.

For vacationers in search of a bargain, Vazquez suggests seven-day hotel and air-fare packages offered by two charter operators, Travel Committee of Owings Mills, Md., and Wainwright Travel of Bethlehem, Pa. Both fly every Saturday from Baltimore/Washington International, and Wainwright flies Sunday from Dulles. You fly away one weekend and return the next.

The two charter firms offer similar packages. Wainwright's August rates range from $449 to $749 per person (double occupancy), depending on the hotel you choose. Eight hotels are listed, including the popular Mahogany Run Tennis and Golf Resort on the island of St. Thomas ($599). There is an additional charge of $70 per person for "tax and service." Included are round-trip air fare, seven nights' lodging and transfers between the hotel and airport.

The summer rates are about $200 per person less than the same package in the winter. For reservations with either charter firm, contact a travel agent.

For information about the U.S. Virgin Islands, including other accommodations: the U.S. Virgin Islands Government Division of Tourism, Suite 270, 1667 K St. NW, Washington, D.C. 20006, (202) 293-3707.

FINDING A HOTEL: When out-of-town friends or business associates ask you for the name of a good hotel in Washington or its suburbs, consider directing them to Capitol Reservations, a new local hotel reservations service.

The firm's founder is Thom Hall, an aide to Sen. Howard Metzenbaum of Ohio from 1977 until January of this year. Hall says he can book callers into more than 50 Washington-area hotels, often at a price cheaper than individuals could get by calling the hotel directly.

Hall saw a need for the service while he was on Capitol Hill. Constituents frequently write or phone congressional offices for advice on where to stay while visiting Washington, he says. He personally discovered the convenience of a central reservation office while traveling in Europe two years ago. Most airports and railway stations in major European cities have hotel booking services.

Hall's is at least the second hotel reservation service available to Washington visitors. The other, formed in the past year, is the D.C. Central Reservation Center, (800) 554-2220 or (202) 289-2220. It offers a choice of about 30 Washington-area hotels.

Hall says his firm has obtained special discount rates at some hotels. And at others, he keeps posted on special weekend or low-season rates.

Room rates in downtown Washington hotels tend to drop in August, he says, and become competitive with rates in suburban hotels. That's because there are fewer business travelers in town during the month. Until Labor Day, a double room in several good downtown hotels ranges from $55 to $75.

For information or reservations: Capitol Reservations, 1201 K St. NW, Washington, D.C. 20005, (202) 842-4187 or (800) VISIT-DC.