Nancy Reagan went to Capitol Hill yesterday to receive an award from a 3-year-old group called Congressional Families for Drug-Free Youth.

"You are the inspiration for our even becoming an organization," cofounder Carolyn Mattingly told the first lady in a brief ceremony held in the historic Old Senate Chamber.

With the wives of 31 House and Senate members looking on, Mattingly presented the group's first "Caring Heart" award to Mrs. Reagan and told her, "Your caring heart shows in the way you work with parents, young people and children, showing them a way out of the trap of drug abuse.

"We never doubted you could have an influence here in America," the wife of Sen. Mack Mattingly (R-Ga.) went on, "but we never imagined you could make such an international impact as we have seen recently."

Describing the scene in Atlanta last month at an international drug-abuse conference attended by Mrs. Reagan and the wives of 15 foreign leaders, Mattingly said: "Since then, you haven't stopped. You have persisted in this task of, in Pope John Paul II's words, ' . . . arresting and eventually eliminating this great social evil' in order to give health and freedom back to young people."

Struggling to get the award, a Steuben crystal heart, out of its box for the benefit of photographers, Mrs. Reagan discarded her prepared remarks to return the compliment.

"I want to thank you for becoming so involved, so active in your home states, encouraging parents groups to form, supporting the kids and getting the community involved. I'm so grateful to you," she said.

Mattingly said later that after noting the impact Mrs. Reagan had on the 1982 PRIDE conference on drug abuse in Atlanta, she began to wonder how to translate that into similar encouragement she and other congressional spouses could take to their home districts.

With B.A. Bensen of Texas, Lana Bethune of Arkansas, Joanne Kemp of New York, Tricia Lott of Mississippi and Emilie Shaw of Florida, Mattingly arranged a meeting with Carlton Turner, presidential special assistant for drug policy.

"We all felt we could have an influence in a smaller way," she said.

A former teacher whose own daughters are grown, Mattingly said the group was not formed because of drug problems among congressional families, but "to take advantage of the influence we have and the resources we have here and at home."

Currently, about 80 spouses are participating and are encouraged to choose a drug-abuse-related project that fits their particular districts.

"Whatever catches the eye of these women, like promoting the antidrug comic books put out by IBM and National Soft Drink Bottlers, is what they pursue," Mattingly said.