Before Capitol Hill enthusiasts become too enamored of the national missile defense system now under consideration by President Clinton, they might want to consider some little-known history that helps explain why deploying such a shield is likely to trigger a new arms race.

In the summer of 1969, while serving as a consultant to the Senate Foreign Relations Committee, I visited a small military compound on South Korean soil, less than 10 miles from the demilitarized zone (DMZ) separating South Korea and its arch enemy, communist North Korea. Inside the compound, the United States was storing nuclear artillery shells for possible use by South Korean forces. I went there because the committee's chairman in those days, Sen. J. William Fulbright (D-Ark.), was examining--for the first time--the implications of the expanding U.S. nuclear presence in other countries.

At the time of my visit, there was no official agreement between Washington and Seoul governing the use of those short-range nuclear weapons, which were first stored there in 1958, or even the sharing of nuclear secrets with South Korea. For obvious reasons, this nuclear artillery deployment was considered a highly classified secret, known to only a few people in the United States and South Korea. But it was far from secret to the North Korean communist regime in Pyongyang.

How had the North Koreans reacted? They had started their own nuclear weapons program. By the mid-1960s, with 40,000 American troops and hundreds of nuclear bombs and shells standing by in the south, North Korea had established a large-scale atomic energy research complex at Yongbyon, employing Soviet-trained nuclear specialists. "Their response was not crazy," said a senior Clinton administration official with longtime experience in the nuclear weapons field.

Of course not. In the world of nuclear politics, it is accepted doctrine that a threatened country will attempt to match strength with strength. During the Cold War, that notion--mutual deterrence--produced a U.S.-Soviet arms race that arms control negotiators are still trying to undo. North Korea has continued its nuclear weapons research over the years, with pauses coming only in the 1990s after the U.S. tactical bombs and shells were removed from the south and after negotiations with the United States led to temporary halts.

The story of the Korean action-reaction is worth telling now as U.S. policymakers assess the fallout from the Senate's rejection of the Comprehensive Test Ban Treaty last month. Just as the North Koreans responded to the introduction of nuclear weapons on their border with their own nuclear program, we should expect reactions from other countries--and not just our enemies--to any resumption of American nuclear testing (as some treaty opponents have recommended).

President Clinton opposed both resumption of nuclear testing and, until recently, a new national missile defense initiative. And administration officials are quick to stress that the proposed missile shield is purely defensive--in the words of Pentagon spokesman Kenneth Bacon, it is designed to "protect the United States against a small attack from what we call an outlaw or rogue nation, such as North Korea or Iran or Iraq."

The president is supposed to make a decision on the missile defense system by next summer. To go ahead, the United States would need to renegotiate the terms of the 1972 Anti-Ballistic Missile Treaty. The Russians and the Chinese have already signaled their opposition to changing the ABM treaty, declaring that doing so could set off a new arms race. European allies of the United States also have expressed complaints about deploying such a system, noting that it would require new early-warning radar systems at U.S. facilities in Britain and Greenland. And what about South Korea, penciled in during a later phase of the project as a possible site for X-Band radar, which is designed to detect and target warheads from North Korea or China aimed at the United States?

These concerns echo the ones the Fulbright committee raised 30 years ago. The placement of U.S. nuclear weapons in countries around the periphery of the Soviet Union and China created "a pattern of deployment which results in arousing deep concern" in those countries, the committee reported in a heavily censored document declassified in November 1970.

Recalling the U.S. reaction in 1962 when Moscow shipped missiles to Cuba, the report noted: "We must assume that the Soviets, as they view our placement of tactical nuclear weapons in countries far closer to their borders than Cuba is to ours, will seek to break out of the nuclear ring that has been drawn around them."

Just two weeks ago, both Russian political and military officials warned that if the Clinton administration goes ahead with the missile defense system, they would respond by increasing their country's supply of long-range strategic missiles and warheads. North Korea can be expected to step up the development and production of long-range ICBMs, inevitably with multiple warheads. And Beijing would undoubtedly put pressure on Seoul should construction of an X-Band radar site in South Korea become a reality.

Of course, the United States isn't the only contributor to the action-reaction cycle. North Korea's Asian neighbors are nervously watching Pyongyang's venture into long-range missiles. Concerned by the development, Japan has vowed to launch its first spy satellites in 2003.

Another element of the Senate committee's inquiry in the late 1960s was the excessive secrecy that surrounded the nuclear deployments. At one point during the investigation, Fulbright asked Maj. Gen. Richard G. Ciccolella, former chief of the U.S. military advisory group to the Republic of China (Taiwan), if the United States maintained nuclear weapons in Taiwan. Ciccolella replied: "I don't know, I really don't know. That was not my business, and I didn't get into that." Sen. Stuart Symington (D-Mo.) later interjected: "So the ranking general on Taiwan, with responsibility for the U.S. position on Taiwan, did not know whether there were any nuclear weapons on Taiwan."

The committee's report noted, "In more than one country, the American ambassador stated that he professed not to know whether nuclear weapons were there. In several [countries] where [weapons] were located, the American ambassadors in question said they did not know what understandings with the host country had been arrived at with respect to their possible use."

This is one area where the past is not being repeated. The Clinton administration has been open on both missile defense and possible renewal of nuclear testing, probably because it has, in the past, opposed both programs. Should a new administration support them, its officials probably would wrap them in secrecy for protection.

Another major difference between 1970 and today was the way the Democratic-controlled Senate committee handled the secret information it obtained from the Republican-led Nixon administration. There were no public hearings on the legality of the South Korean deployments. The forward-based artillery shells were subsequently moved back to more secure air bases in the central part of the country that already held tactical nuclear bombs. The required nuclear secret-sharing agreement was negotiated and signed, all without publicity. If recent Republican wide-ranging investigations into the sending of Iranian arms to Bosnia, Chinese campaign contributions, launching of U.S. satellites in China and alleged Chinese espionage at U.S. nuclear labs are any guide, that kind of past congressional restraint on sensitive foreign policy issues would probably not exist in today's partisan atmosphere.

The Korean experience also reminds us how much the world has changed in 30 years. Take the question of security.

Those nuclear artillery shells in South Korea--some of which had the explosive power of 10,000 tons of TNT, or almost two-thirds the strength of the Hiroshima bomb--were kept in concrete bunkers. Security for these most sensitive nuclear weapons was primarily the responsibility of the roughly 30 American servicemen living in the compound, which was surrounded by two barbed-wire fences, between which ran a team of German shepherd guard dogs.

In the event of trouble, the plan was to call for help from a company of South Korean soldiers at an officers' training school less than a mile away down a one-lane road. Think of what the General Accounting Office or congressional investigators would say today about that arrangement.

We live in a different world now, of course. Heightened concerns about terrorism--and the recent bombings of U.S. embassies in Kenya and Tanzania--have taught us that any U.S. facility abroad is a target and that no U.S. facility is invulnerable. In a larger sense, that's the main lesson: Whatever the United States does, wherever its presence is felt, its actions don't occur in a vacuum. In the world of missiles, missile defenses, nuclear physics and nuclear politics, action-reaction is still the norm.

Washington Post reporter Walter Pincus has written about national security issues since 1975.