While President Reagan is attending the May 2-4 economic summit of industrialized nations in Bonn, Nancy Reagan will be attending a summit of her own -- this one at the Vatican.

Yesterday, it became official that the first lady's independent schedule in Europe, where the Reagans will make state visits to West Germany, Spain and Portugal, will include a private audience with Pope John Paul II to discuss the effect of drug abuse in international problems.

According to Jennefer Hirshberg, the first lady's press secretary, Mrs. Reagan's trip to Italy also will include visiting Progetto Uomo, an organization for the rehabilitation of drug abuse victims that has opened branches throughout the country.

Meanwhile, back in Washington, nobody is yet calling it "Nancy Reagan's White House Summit on Drug Abuse," but with the wives of leaders of 17 foreign countries coming to town April 24, planning the logistics for it is beginning to assume summit proportions.

"Never in our wildest dreams did we expect the response we got," says one White House staffer.

The timing, though, could have been better. Both the State Department and the National Security Council, helping with arrangements, are up to their ears in planning their own summits.

Says the White House source thinking of the myriad details, such as how many interpreters will be needed, "It's a nightmare."