SOME PEOPLE think cherry blossoms mean spring in Washington. Real Washingtonians know the true sign of spring is the advent of the house and garden tour season. Washington is the center of a five state area, graced with some of the most historic houses and gardens in the country. This month and next, many of these fine homes and estates, in the District of Columbia, Maryland, Virginia, West Virginia and Delaware, are open to the public for a donation to charity. Leave the youngsters and spike heels at home -- you've got a lot of ground to cover:

The 53rd Annual Georgetown Garden Tour will be April 25, 10:30 a.m.-5 p.m. Twelve gardens including those belonging to Prospect House and Mackall Square House as well as Dumbarton Oaks Gardens will be shown. Tickets are $8 (children under 12 go free) and can be bought at the Georgetown Children's House, 3224 N St. NW, or at the any of the garden gates. The tour will benefit the Georgetown Children's House, a day-care center for children from low-income families. Limited shuttle service is available. Tea and coffee will be served at the Children's House between 11:30 a.m. and 4:30 p.m. Call 333-4953 for ticket and other information.

The Fifth Annual Cleveland Park House Tour will take place April 26, 1-5 p.m. to benefit the National Child Research Center, a non-profit independent school for children 2 1/2 through kindergarten. The tour of eight homes includes "Rosedale," the 18th-century Federalist farmhouse, as well as the 1937 Waldron Faulkner home. (See FUNCTION on Page 1 for a description of the Whitney Adams/David Copus house designed by Dickson Carroll). The walking tour begins with an open house at the Georgian Revival school, 3209 Highland Place NW. Tickets are $7 in advance and $8 on the day of the tour. Call 363-8777 for more information.

The 54th Annual Georgetown House Tour will be May 2 and 3. Seven homes will be shown each day, noon-5 p.m. Tea will be served at St. John's Church, 3240 O St. NW, from 2-6 p.m. Tickets ($10) go on sale at the church at 11 a.m. the day of each tour or can be bought at any one of the homes on the tour. Baby-sitting is available. Call 496-1152 for reservations.

The embassies of Australia, Chile, Guatemala, Panama and South Africa, as well as the Apostolic Delegation, are on this year's Annual Goodwill Industries Guild Embassy Tour on Saturday, May 9, 11 a.m.-5:30 p.m. Tickets are $12 a person (tax deductible) with discounts available for groups of 25 or more ($10).

All embassies are within walking distance, but shuttle-bus service will be provided, as well as complimentary tea at the New Zealand embassy and a souvenir booklet with interior pictures of the embassies. Lunch will be served at the National Presbyterian Church, Nebraska Avenue NW, for $6 per person. Tickets must be bought before May 1 and can be reserved by calling (301) 530-4318 or by writing Mrs. William Rigdon, 5406 McKinley St., Bethesda, 20034.

The 24th Annual Capitol Hill House and Garden Tour is set for May 10, 1-6 p.m. The tour, to benefit the Capitol Hill Restoration Society, will kick off National Trust Preservation Week. Free shuttle service between houses will be provided. Tickets are $9 in advance and $10 on the day of the tour. Tickets may be bought by mail from the society, 1002 Pennsylvania Ave. SE or from a number of Capitol Hill merchants. Call 543-0425 for details.

The Kalorama Triangle House Tour will take place May 17, 1-5 p.m., with tea following from 4 to 6 p.m. at the Middendorf Lane Gallery. Tickets ($6) may be bought the day of the tour at 2337 Ashmead Pl. NW or at 1922 Calvert St. NW. Half price tickets are available for children under 12 and for senior citizens. Tickets may also be purchased by writing (before May 11) to: Jeffrey Jacobson, 1930 Biltmore St. NW, Apt. 3, Washington, D.C. 20009. for details call 667-1724, after 6:30 p.m. Virginia

Historic Garden Week in Virginia will hold its spring tours April 18-26. The 199 private houses and 52 shrines and landmarks in 34 regions range from Fairfax to Lexington. The Alexandria tour on April 25 includes the passive solar-heated Wysong residence (see Form on Page 1). Tours and dates: Albermarle, April 18-April 25 Hanover, April 18 Portsmouth, April 18 Chatham, April 19 Leesburg-Loudown, April 19-20 Charlottesville, April 20-22 and 24 Fredericksburg, April 21 James River Plantations, April 21-25 Lexington, April 21 Lynchburg, April 21 Mecklenburg-Brunswick, April 21 Petersburg, April 21 Richmond, April 21-23 Virginia Beach Resort area, April 21 and 23 Williamsburg, April 21 Harrisonburg, April 22 Martinsville, April 22 Newport News, April 22 Norfolk, April 22 Urbanna, April 22 Warrenton, April 22-23 Danville, April 23 Eastern Shore, April 24-25 Gloucester, April 24-25 Goochland, April 24-26 Blacksburg, April 25-26 Rapidan Village, April 25-26 Warren County, April 25-26 Waynesboro, April 25-26 Winchester-Frederick County, April 25-26

Tickets rnage from $3 to $10, depending on the area, and can be bought at the first house on the tour -- no tickets will be sold in advance. A 62-page booklet about the houses, giving the addresses and dates of the tours, is available at the Virginia State Travel Service, 1906 17th St. NW (293-5350); the Alexandria Bicentennial Commission, 201 S. Washington St., Alexandria; and the Alexandria Tourist Council, 221 King St., Alexandria.

"Since the cost of the mailings have gone up to 92 cents per booklet, we're asking for donations of 50 cents to help us pay for the publication," apologizes spokesperson Charlotte Massie.

Doorways to Old Virginia, 513 S. Royal St., Alexandria, will sponsor a tour to the James River Plantations -- Sherwood Forest, Shirley, Westover and Riverview Farm -- April 21, 7 a.m.-6 p.m. The tour will leave from Christ Church, 100 N. Columbus St., Alexandria. Cost: $40 -- includes admissions, transportation and lunch. To register, call 548-0100.

The Energy House Tour of Fairfax County is set for May 17, 11 a.m.-5 p.m. Sponsored by the League of Women Voters, the tour features active and passive solar homes. Tickets cost $5 and are available at all branches of Coldwell Banker/Routh Robbins -- Realtors or by mail from the League, 7704 Falstaff Rd., McLean, Va. 22102. Call (703) 281-0776 after May 1 for details. Maryland

The 28th Annual Landon Azalea Garden Festival will be May 1-3 at Landon School, 6101 Wilson Lane in Bethesda. Guests will be able to wander over the 73 wooded acres to view more than 15,000 azaleas, rhododendrons, peonies and wildflowers. An antique show by 30 dealers; a sale of original paintings by Elizabeth Boyd and Trudie Davis; a flower-arranging competition; a needlepoint sale, and a tour of the 180-year-old antique-filled Farmhouse located on the school grounds are other events. Admission to the festival is free. Hours: 10 a.m.-5 p.m. each day.

Four appraisers from Christie's auction house will apprise items on May 2, 10 a.m.-4 p.m. They are: David Ober, Christie's representative in Washington; Charles Beyer, vice president of Christie's and its furniture expert; Colin Sheaf, porcelain expert; and Anthony Phillips, silver expert. No coins, jewelry, books or pre-Columbian art will be apprised. Photographs are encouraged for large objects. Fees: $6 for one object; $10 for two.

The 44th Annual Maryland House and Garden Pilgrimage will be April 25-May 9.

The Anne Arundel County tour on April 25 will include a visit to the governor's mansion in Annapolis and a tea given by Governor and Mrs. Hughes. Other Maryland tours include: Calvert County, April 26 Wicomico County, May 2 Dorchester County, May 3 Carroll County, May 5 Bolton Hill in Baltimore, May 6 Western Run Valleys in Baltimore County, May 7 Frederick County, May 8 Kent County, May 9

A fee of $8 will be charged for each day of the tour. The price includes a booklet on the pilgrimage's homes and gardens. For tickets and information call (301) 821-6933 between 9 a.m.-1 p.m. weekdays.

Doorways to Old Virginia will also tour the Maryland Garden Pilgrimage in Chestertown, May 9. The trip includes visits to 18th- and 19th-century county estates and lunch at the Emmanuel Episcopal Church. Fee: $40. To register, call 548-0100.

The ninth annual Takoma Park House and Garden Tour will take place May 3, 1-5 p.m. Advance tickets are $3.50 and can be bought from the Takoma Park Recreation Department, Municipal Building, 7500 Maple Ave., Takoma Park. On the day of the tour, tickets are $4.50, available after 12:30 p.m. at the same address. Free busses will leave from the Municipal Building. For details call 270-4048 (days) and 270-5798 (evenings). West Virginia

The 26th House and Garden Tour of Historic Shepherdstown, Martinsburg, Charles Town and Harpers Ferry will be April 25 and 26, 10 a.m.-6 p.m. The Shenandoah-Potomac Garden Council is sponsor. The tour includes "Cedar Oaks," the restored Martinsburg home of Mr. and Mrs. D.A. Sutherland. Seven other homes are on the tour, as well as the Jefferson County Museum and the Harpers House. Tickets are on sale at all houses on the tour, $6 for entire tour, $1.50 for single admission. For more information, write TOUR, P.O. Box 40, Shepherdstown, W.Va. 25443. Delaware

Spring tours at Winterthur Museum and Garden near Wilmington, Del., begin Wednesday and continue through June 7. Visitors can walk or ride through the blooming gardens and view the many rooms of the mansion Tuesday-Saturday, 10 a.m.-4 p.m. and Sunday, noon-4 p.m. Admission is $5 for adults, $3.75 for students, senior citizens and groups, children under 12 free. Winterthur is on Rt. 52, six miles northwest of Wilmington.Call (302) 654-1548 for details.