Nancy Reagan brought her international crusade against drug abuse to Italy today, saying she wants to hear what Pope John Paul II has to say about saving young people from addiction.

The first lady flew here from Bonn, West Germany, for a 46-hour visit while President Reagan attends the economic summit. At the Vatican on Saturday, Mrs. Reagan said, she plans to discuss with the pope last week's White House antidrug conference for the wives of 17 foreign leaders.

"I think he's been briefed -- or has a report of the whole day being with the first ladies, so that we may hopefully discuss it," she told reporters flying with her aboard an Air Force plane.

She said that for the most part, however, she was going to listen to what the pope had to say. Asked if she thought the pontiff a symbol in the fight against drug abuse, she said she did, adding, "I think he is important in the world for anything."

She noted she feels "an extra affinity" for the pope "because of the closeness of the two attempted assassinations." They had talked about the attempts on the pope's and president's lives in June 1982 after the economic summit at Versailles, France.

She said that conversation was similar to one the president and the late Cardinal Terence Cooke of New York had after her husband came home from the hospital. Cooke told Reagan, " 'You know, Mr. President, God was really sitting on your shoulder that day.' " And she said her husband replied that he knew it and had thought about it a lot and had decided that whatever days were left to him "belong to Him."

She said she was also looking forward to visiting a drug rehabilitation center at Castel Gandolfo and to meeting more parent groups involved in drug abuse.

Other topics she touched upon during her 1 1/2-hour flight from Germany included:

* The visit she and the president will make to Bitburg on Sunday. "I don't have any comment on that," she said, refusing to get into a discussion about it.

* The Reagan's feast-fast diet to counter jet lag. "I really don't think it makes any difference -- my husband thinks it makes a difference."

* Her morning visit to a parents group in Bonn where drug abuse was discussed. "The thing that really strikes you the most are the similarities in stories, which only goes to prove the validity of having the White House meeting we had. The problems are exactly the same."

At Rome's Ciampino Military Airport, the first lady was met by Anna Craxi, wife of Italy's prime minister; Anne-Marie Petrignani, wife of Italy's ambassador to the United States; U.S. Ambassador to Italy Maxwell Rabb and his wife, Ruth, and U.S. Ambassador to the Holy See William Wilson and his wife, Betty. Mrs. Reagan was accompanied by a staff of 10.

Tomorrow, Mrs. Reagan's first stop will be the Quirinale Palace, a former papal summer residence that became a royal residence in 1870. Italy's 89-year-old president, Sandro Pertini, lives there and is giving a lunch for the first lady.

In the afternoon, Mrs. Reagan will visit the San Carlo Therapeutic Center, a treatment and rehabilitation facility for drug addicts, at Castel Gandolfo. Anna Craxi will present her with an award for her work against drug abuse. The only other recipients are Pertini and Pope John Paul II.

Tomorrow night the Rabbs will entertain Mrs. Reagan at a black-tie dinner at their residence, Villa Taverna. The U.S. Embassy here has not released a guest list for the dinner, but among the expected guests are Gregory Peck, fashion designers Emilio Pucci, Valentino and Laura Biagiotti, Fiat's Johnny Agnelli and actresses Sophia Loren and Gina Lollobrigida.