PRESERVATION CAN be many things: planting gardens, keeping out strip mining, lobbying in Congress, putting up the money to buy an architecturally famous house, researching your own neighborhood.

The National Trust for Historic Preservation honored almost two dozen groups and people for such work last week at a lunch in the Decatur House garden. The presentations were made by James Biddle, president of the trust, and Interior Secretary Cecil D. Andrus.

In Virginia, gardens with stately brick walks and old-fashioned flowers recall the state's long horticultural history. Some 24 of these gardens - surrounding historic homes such as Woodlawn and Gunston Hall near Washington and historic buildings including the Lee Chapel at Lexington - were established by the Garden Club of Virginia. Money to pay for roses, brick, fertilizer and gardeners comes from the annual garden week tour, which raises about $100,000. The 2,800-member club established more than a half century ago was one of the winners of the David E. Finley Award for outstanding achievement in historic preservation at the regional level.

In Louisa County, Va., Historic Green Springs, Inc., was organized when the state proposed to build a prison on 200 acres in the heart of the rolling countryside. Other interests had strip mining in mind. The organization, through court battles, got the construction halted and also blocked the proposed zoning change that would have allowed strip mining. Half of the district's 14,000 acres - including many 18th and 19th-century manor houses and their settings - are now protected by federal scenic easements, donated by 38 landowners. The organization also received a Finley award.

In Washington, Nellie L. Longsworth, executive director of the national lobbying group, Preservation Action, counts among the accomplishments of her three-person staff successful lobbying for the 1976 Historic Structures Tax Act, which provided incentives to save commercial buildings listed on the National Register, and the $10-million National Historic Preservation Fund administered by the Interior Department, passed in 1977. Longsworth also is responsible for publishing a quarterly newsletter Alert, which keeps historic organizations infromed on legislation. She received a Gordon Gray Award for achievement in support of preservation.

In Baltimore, Mayor William D. Schaefer; Edward R. Oppel, head of the Bureau of Construction Managemernt and Robert C. Embry Jr., former commissioner of the Baltimore Department of Housing and Community Development and now assistant secretary of the Department of Housing and Urban Development, were largely responsible for preserving Baltimore's historic structures, especially the city hall, and integrating them with the new buildings downtown. They are to receive a public service award to be presented in June.

Other winners this year were:

Dr. John L. Cotton of Philadelphia, whose 35 years as an archeologist included discoveries about Jamestown, Va., the first English settlement, and founding the Society for Historical Archeology.

Gray D. Boone of Tuscaloosa, Ala., editor and publisher of Antique Monthly and The Gray Letter, national publications dealing with preservation, antiques and decorative arts.

Mystic Seaport, Inc., Mystic, Conn., the only museum in the world with a shipyard for preserving, displaying and interpreting historic vessels.

Roosevelt University and Mrs. John V. Spachner of Chicago, Ill., for restoring and interpreting the auditorium building and theater, designed by architects Dankmar Adler and Louis Sullivan.

The City of Cambridge, Mass., for publishing the Cambridge Historical Commission's "Survey of Architectural History in Cambridge," considered one of the best city records.

Avenue Bank and Trust Co., First Bank of Oak Park, Oak Park Trust and Savings Bank, and Suburban Trust and Savings Bank (Illinois) for putting up the money to buy the Frank Lloyd Wright home and studio, now preserved as a house museum.

Alderson, W. Va., population 1,200, which preserved a 1914 bridge across the Greenbrier River no longer used for automobile traffic as a pedestrian thoroughfare.

The Cleveland Trust Co. and the Union Commerce Bank of Cleveland for restoring two beaux-arts buildings still used as banks.

Rosemary Stroub Davison of Florisant, Mo., for preserving a schoolhouse, several homes, a railroad station and a cemetery. She also helped pass the town's preservation legislation.

Whatcom County Park and Recreation Board of Bellingham, Wash., for restoring a late 19th-century farm and homestead as a museum.

Moon Landrieu, former mayor of New Orleans, for starting a preservation program that goes beyond the French Quarter to other old neighborhoods. He also established the landmarks commission.

Henry C. Chambers, mayor of Beaufort, S.C., for helping rescue the Beaufort River from pollution; constructing a waterfront mall and greenbelt; establishing a revolving fund for the Historic Beaufort Foundation and protective regulations for the historic district and an architectural review board.

Richard H. Chambers of San Francisco, chief judge of the Ninth Circuit, U.S. Court of Appeals, for his part in preserving the U.S. Post Office and Courthouse and the U.S. Mint in San Francisco.