The loss of Galaxy IV, one of about 250 commercial satellites currently operational, drew our attention to the ever-increasing linkage between everyday life and systems in space. It also reminded us of how fragile and vulnerable those systems are. Early reports of hacker sabotage turned out to be wrong. Galaxy IV's problem was technical, a processor that failed to switch on. It could have been the work of a hacker or an adversary, though, and next time it may be.

What we have seen so far is the first wave of a massive migration of civil, commercial, and military functions into space. Most of the 1,500 new satellites going up in the next five years will be commercial ones. The space industry is growing at a rate of 20 percent a year.

US Space Command predicts that our dependence on space capabilities in the 21st century will rival our dependence on electricity and oil in the 19th and 20th centuries.

Space is fast becoming an area of vital national interest. When the nation's interests in space are challenged--and, sooner or later, they will be--the nation will expect its armed forces to be ready.

Unfortunately, the commercial surge in space is not matched by preparations for the defense of space. According to the Office of Management and Budget, defense spending on space activities fell by 52 percent between 1989 and 1995.

The main constraints, however, are political. We are nominally committed to space control, the ability of the United States and its allies to reach space and operate freely there while denying those capabilities to an adversary. In actuality, our commitment is hedged by a host of policies, treaties, and agreements that restrict military operations in space.

Space Command is effectively limited to information, surveillance, reconnaissance, communications, and other support missions. It has neither the means nor the charter for offensive operations to directly defend our interests in space. The very notion of weapons in space is contrary to national policy.

In January, 43 retired generals and admirals wrote to President Clinton saying that the United States must dominate space in wartime and that we must have "such crucial capabilities as space-based missile defenses" and be able to "neutralize hostile spacecraft in time of war."

Pressed by members of Congress and others, the Administration has restated its commitment to space control, but our national policy has not changed.

The defense of space is further complicated by differences in civil and military priorities. Space is a booming market with strong commercial interests that center on trade, exports, and the open availability of technology. It is difficult to withhold capabilities from that market, especially if they are of great value to civil users.

High-resolution imagery from satellites has already gone commercial. So has the Navstar Global Positioning System, which was developed by the US Air Force. It is now standard equipment for fishermen and hikers. Soon, rescue squads will begin using it to find cellular phone users in distress. GPS is also in use by China to improve the accuracy of its weapons.

Earlier this year, the Defense Intelligence Agency warned Congress that US military dominance in space is eroding. Space Command forecasts that by 2020, if not sooner, "adversaries will share the high ground of space with the United States and its allies."

Gen. Howell M. Estes III, commander in chief of US Space Command and commander of Air Force Space Command, believes that "some day in the not so distant future, space will have evolved to the point where the movement of terrestrial forces will be accomplished only at the pleasure of space forces, much the same way that the movement of land and sea forces today can only be accomplished at the pleasure of air forces."

In a new long-range plan published in April, US Space Command says we should begin contingency preparations now in case "our civilian leadership [should] later decide that the application of force from space is in our national interest." That proposal is eminently sensible.

It is beyond question that critical elements of our destiny lie in space. We can no more isolate ourselves from interests there than we can from our interests in Europe or Asia.

Nor is there any real doubt--no matter how discomforting the reality of it may be for our political leaders to accept--that, when push comes to shove, we will have no choice but to defend our vital interests in space.

If we expect the armed forces to be ready when that time comes, we had better begin making some changes now in our national policies and plans.