After a year of study, there has been talk in Congress and federal agencies the past few days about the vulnerability of the United States to terrorist attacks, particularly electric power and telecommunication systems.

Advanced technology and the growing use of interdependent, centralized systems make it easy to carry out "catastrophic" terrorist attacks, investigators told the Senate Governmental Affairs Committee this week.There is no doubt that the United States has always been vulnerable to terrorist sabotage. The country is too big, too free, too open, too unguarded, too dependent on technology - too civilized, if you will.

Under such circumstances, there is simply no way to prevent attacks by determined terrorists, although the recent conviction of a Libyan-paid Japanese Red Army member - arrested before he could explode any of the bombs he was carrying - shows the United States is not totally ineffectual.

Yet the threat may be over-blown. For one thing, the very size of America - one of its security weaknesses - also is a deterrent. The country is clearly too big for small bands of terrorists to actually shut it down.

Determined terrorists could do significant damage to communication or power systems in a specific locality, or perhaps even over a wider region. But because of the vast size of the United States, sabotage attempts would tend to be self-limiting.

Even the experts disagree over the vulnerability of such systems. A deputy manager of the National Communications System, a federal agency entrusted with safeguarding government communications, says the nation's telecommunucations are "diverse, robust and redundant" making them hard to disrupt.

The potential threat of terrorist attack has been greater in the past. For example, the Iran-Iraq war was raging, Israel was occupying half of Lebanon, and the United States was bombing Libya - all at the same time. The United States was vilified in all three situations, but little in the way of terrorist activities could be detected in the United States.

All of those situations have calmed or ended, although circumstances could make America more of a target in the future. However, the fact remains that for all its supposed vulnerability, the United States has not been a major target of foreign terrorists.

There have been overseas incidents, such as the bombing of the Pan Am jet, but those are not in the same category as terrorist acts within the United States that are worrying some security experts.

Certainly, crucial domestic industries need to be aware of security problems and to update measures to deal with them. But there appears little reason for panic or for some kind of Big Brother protective system to be imposed by the federal government.