At the height of the Cold War, the United States secretly deployed thousands of nuclear weapons in 15 foreign countries, introducing bombs into some nations--such as Iceland and Morocco--without the knowledge of their leaders, according to a study published today in the Bulletin of the Atomic Scientists.

Although many of the deployments have previously been revealed, the study contains the most comprehensive list of U.S. nuclear weapons and the dates that they were placed in locations outside the 48 contiguous United States, including Hawaii, Alaska and some Pacific islands under U.S. control as well as foreign countries.

The list is based largely on the Defense Department's own history of such deployments from 1945 to 1977. Written in 1978, the Pentagon history was partially declassified this year in response to a Freedom of Information Act request from the Natural Resources Defense Council, a private research group in Washington.

The Pentagon blacked out the names of all but three countries: Cuba, West Germany and the United Kingdom. But because the locations were listed in alphabetical order and the authors of the study had a wealth of corroborating data from other sources, they believe they were able to identify 12 other countries, naming some for the first time.

The study reveals, for example, that nuclear bombs were stored from 1956 to 1959 at a U.S. base in Iceland, which has a strong non-nuclear tradition and publicly opposed many of NATO's nuclear policies.

From December 1961 until mid-1963, a period that included the Cuban missile crisis, the United States kept "nuclear-capable" depth charges at its base on Guantanamo Bay, Cuba. These anti-submarine weapons technically were not nuclear bombs, because they were stored without their vital plutonium "pits." But the pits, which were stored in Florida, could be inserted quickly in the event of war.

Without telling the French government, President Harry S. Truman in January 1952 also authorized the storage of nuclear-capable bombs, lacking only the fissile component, on Strategic Air Command bases in French Morocco. Complete nuclear bombs, intended for delivery by U.S. warplanes against the Soviet Union, were deployed in Morocco from 1954 to 1963.

One of the study's authors, Robert S. Norris, a senior research analyst at the Natural Resources Defense Council, said yesterday he has a U.S. government document that says France "should not be informed" about the weapons in Morocco, which was a French and Spanish protectorate at the time. The Moroccan government apparently was informed after it gained independence in 1956.

Contrary to most scholars' assumptions, complete U.S. nuclear weapons were deployed in Morocco even before they were placed in Britain, according to Norris and his co-authors, William M. Arkin and William Burr.

Nuclear-capable bombs, minus their essential uranium or plutonium, also were sent to Japan, the country with the strongest anti-nuclear feelings. They were deployed by the Eisenhower administration during the U.S.-China crisis over the Taiwan straits in 1954-55 and were intended for nuclear operations against China or Russia in the event of war, the authors say.

Beginning at about the same time, complete nuclear bombs, artillery shells and missile warheads were placed in Alaska, Hawaii and Okinawa. Later in the 1950s, such weapons were deployed in South Korea, the Philippines and Taiwan, according to the study. Norris said yesterday it was not clear whether those countries were informed of the initial deployments.

Because of domestic sensitivities, foreign leaders often have not wanted to acknowledge the presence of U.S. nuclear weapons on their soil, and it is difficult for historians to determine if, or when, they received formal notification.

In the past, such revelations have sometimes caused a furor. Five years ago, the United States acknowledged that it had kept nuclear weapons from 1958 to 1965 at Thule Air Base in Greenland, part of the realm of Denmark, a stridently non-nuclear country. The disclosure set off a Danish political scandal, dubbed "Thulegate."

Fridrick Jonsson, first secretary at the Embassy of Iceland in Washington, said yesterday that his government has previously been asked about U.S. nuclear weapons and has always said it "had not been aware of the presence of nuclear weapons in Iceland."

A Pentagon spokesman said the Defense Department would adhere to its traditional policy of neither confirming nor denying U.S. nuclear deployments overseas.

The authors of the study believe they have been unable to identify only one location where nuclear weapons were deployed outside the continental United States. The mystery site, which falls alphabetically between Canada and Cuba, hosted nuclear weapons from 1956 to 1965, according to the study.

Although most of the U.S. nuclear bombs deployed overseas were intended for use by the U.S. military, the study says that as many as 40 percent of the weapons in Europe were for use by NATO allies. These included not only West German and British aircraft, but also planes flown by Greek and Turkish pilots. The actual bombs, however, remained under American custody and could not be armed without the participation of a U.S. serviceman.

At the peak in the late 1960s, more than half of the 7,000 U.S. nuclear weapons in Europe were stored in West Germany. In Asia, the Japanese island of Okinawa was the major storage point, holding as many as 1,000 U.S. nuclear weapons at a time between 1954 and 1972.

The numbers began to drop after the Vietnam War, and by the end of the 1970s, the only U.S. nuclear weapons left in the Far East were in South Korea. They were withdrawn in 1991.

Today, the study says, the United States has fewer than 150 nuclear bombs at 10 air bases in seven NATO countries. But it "is still the only country with nuclear weapons outside its borders," according to Norris.