WASHINGTON (AP) _ President Reagan on Monay presented the nation's top awards for volunteer work to a wildlife specialist, a postal union and a retired couple that uses an 18-wheel truck to help disaster victims.

''You're champion givers ... people of heart, selflessness, examples to the entire nation,'' Reagan said as he presented the Presidential Volunteer Action Awards. ''I can think of nothing finer to say about our country than that it has produced men and women like you, true heroes of the heart.''

Reagan told the receipients they should take a lesson from award winners Gilbert and Madeline Laake, who drive a Red Cross truck into disaster zones to help organize relief efforts.

''I just can't resist. ... I just want to say 'keep on truckin,''' Reagan said with a grin, evoking a chuckle from his audience.

Vincent Sombrotto, president of the National Association of Letter Carriers, slipped Reagan a folded paper that appeared to be a letter. The item, which the president put into his pocket without reading, was about a postman who had given his life to save two children during a Pennsylvania tornado, Sombrotto said later.

The presidential awards went to 15 individuals, groups and national organizations, as well as three corporations and the postal union. The awards were created in 1982 to call attention to the contributions of the nation's volunteers. They are co-sponsored by Volunteer, a private non-profit organization, and ACTION, the federal agency for volunteer service.

The Laakes, from Bellevue, Ky., ''spent 126 days away from home on relief operations'' during the past year, noted a White House announcement of the awards.

The National Association of Letter Carriers was honored for devising the Carrier Alert project to monitor the well-being of elderly and disabled adults who live alone and may not be able to summon help in the event of illness or accident.

Raymond J. Moore, the volunteer director of the Wildlife Rescue and Rehabilitation in Hillsborough and Pinellas counties, Fla., ''traveled over 20,000 miles responding to calls to assist injured animals throughout the state'' in 1985 and has organized numerous groups of court-referred volunteers to assist wounded animals, the awards announcement said.

Other recipients included:

-The Oregon Shakesperean Festival Organization of Ashland, Ore., a non- profit repertory theater organization that operates three theaters which play to nearly 400,000 people during its February-to-November season.

-The Boys Choir of Harlem, of New York, N.Y., a 100-member choir founded in 1975 to provide special musical training, and educational and personal counseling to inner-city children ages 9 to 19.

-Carol Sasaki, of Pullman, Wash., who founded H.O.M.E, which assists low income women and welfare recipients to complete their education.

-Kimi Gray, of Washington, D.C., founder of College Here We Come, a program that assists young people in public housing projects get into college.

-Jerome H. Stone, of Chicago, founder of the Alzheimer's Disease and Related Disorders Association, which helps focus attention on the disease and raises funds for helping victims and families cope.

-Operation Santa Claus in Sacramento, Calif., a project of the Sacramento Army Depot that provides family assistance to as many as 9,000 needy military and civilian families.

-Anthony Barracca of Apopka, Fla., who has helped provide food and other assistance to a local mission, childrens' home, migrant worker camps and the Salvation Army for the past three years.

-Gloria Allred of Los Angeles, Calif., who developed Project Amnesty as a pilot project in five California counties to increase child support payments.

-Heifer Project International, of Little Rock, Ark.,, which has sent approximately 74,000 animals and nearly 2 million chickens or other poultry to needy people in more than 33 states and 100 nations.

-Aid Association for Lutherans of Appleton, Wis., a fraternal benefit society which has provided its 1.3 million members with resources to conduct humanitarian, service, social and educational programs.

-Volunteer Connection of Dallas, Texas, which was launched to help promote volunteer action for local agencies.

-Long Island Associaion to Increase Security in Our Neighborhoods, of New Hyde Park, N.Y., which has involved local citizens in an extensive crime prevention and public education effort.

-Louis Leeder, of Brooklyn, N.Y., who helped found the National Association for the Jewish Poor to help poor, elderly homebound Jewish people in the New York City area.

-The Mutual Benefit Companies of Kansas City, Mo., which combined company resources with employee volunteers to help revitalize neighborhoods in decline.

-Chesapeake and Potomac Telephone of West Virginia, of Charleston, which initiated a number of economic development programs in West Virginia.

-Security Pacific National Bank of Los Angeles, Calif., which set up volunteer programs to assist over 300 community organizations and 200 school districts by helping improve educational and job training skills.