In an emotional ceremony today, Nancy Reagan told the residents of a drug program at Castel Gandolfo that they must guard the "little light inside of you."

"It burns only for you," she said. "Sometimes it glows brilliantly -- remember those days? Sometimes it flickers. Sometimes it nearly goes out. And when it gets low, as much as your family and friends yearn to help it grow brighter, you must tend it yourself. And that is why you are here."

The first lady, who appeared near tears at times, received an award from the drug rehabilitation program, which has the backing of Pope John Paul II, for her worldwide influence in efforts to eradicate drug abuse.

The award, previously presented to the pope and Italy's President Sandro Pertini, highlighted the first lady's visit here, which includes a private audience with the pontiff.

Mrs. Reagan came close to crying when the center's founder, Don Mario Picchi, thanked her for her "unfailing commitment to promoting an extensive program of prevention and rehabilitation throughout the world."

Another time tears seemed near was toward the end of her speech accepting the award. She regained her composure in time to try out a little Italian on her hosts, saying, "Voglio bene a puppi" ("I love you all").

The ceremony was held in the garden of a historic villa at Castel Gandolfo, summer home of the popes. The award, a two-foot-tall bronze sculpture representing the Italian Solidarity Center's "Progetto Uomo" (Project Mankind) was a replica of a statue in the garden.

Among the audience of several hundred guests were the center's 70 residents who are undergoing rehabilitation and treatment.

"This place is bathed in hope and promise," Mrs. Reagan said of the center, one of Italy's best known in the field of drug therapy. "Partly because His Holiness is the donor. Partly because of what you are accomplishing here."

During an indoor part of the program, she heard several residents tell her how they happened to be at the center. Seated in a semicircle with them on small wooden stools, she clasped a single pink rose matching the pink in her turquoise-and-pink suit and listened to an interpreter simultaneously relate to her the residents' stories.

The room was jammed with onlookers, including Anna Craxi, wife of Italy's prime minister; U.S. Ambassador Maxwell Rabb and his wife Ruth; fashion designer Laura Biagiotti; and Anne Merete Petrignani, wife of Italy's ambassador to the United States.

Italian and American photographers jostled for position in an unusually gentlemanly manner in the tight space allotted them. When one resident asked Mrs. Reagan how she happened to become interested in drug abuse, her answers were almost drowned out by the clicking of cameras.

"I think this is the most dangerous problem we have," she said, summing up her answer.

A resident who identified herself as Cinzia told the first lady that "I shot up for five years," and only arrived at the center "because I didn't have any values anymore . . . I gave no value to life and, quite simply, because I did not have the courage to live."

Claudio, another resident, said he had used heroin for 12 years and "I never really thought I could quit. I thought only death could stop me from this life."

In welcoming Mrs. Reagan, one resident said, "No one can be more grateful to you than we are -- we who have known the darkest hell of drug abuse -- for your initiatives aimed at making our society know, understand and conduct a vigorous action of prevention, countering the scandal of drug abuse with values of true civilization.

"At a time of crisis of values," the resident continued, "we young people feel the need to rediscover a moral and civil, spiritual and political path which will lead us back to life, help us live fully and encourage us to build a better future for all."

Picchi told Mrs. Reagan that the award was created "as a renewed act of faith in man, the protagonist of his own life."

He said the pope, who donated the hilltop villa as the center's headquarters, was the award's first recipient as "an unflinching advocate of man's rights, of the rights of all men, particularly those who are needy, wretched, rejected by life."

Pertini was the second recipient "for his exemplary activity and for the contribution he has endeavored to give to the construction of a healthier, more human society," Picchi said.

En route to the center, about 15 miles southwest of Rome, Mrs. Reagan stopped in for lunch with Pertini at the Quirinale Palace.

Not present was Pertini's wife, Carla, a part-time worker with drug addicts here. A woman who shuns the limelight, she has made a practice during Pertini's seven years in office of maintaining her own identity and schedule.

Before that event, the first lady dropped in on industrialist Giovanni Agnelli, chairman of the Fiat auto company.

Tonight, the Rabbs entertained her at a black-tie dinner, where the guests were expected to include movie stars, fashion designers and Italian industrialists.

Designer Valentino, who will be a guest, let it be known through a spokesman today that Ruth Rabb and some of her guests, including Sophia Loren, will be wearing his gowns.

Mrs. Reagan returns to Bonn Saturday after her private audience with the pope.