After studying the issue for a year, a joint committee of Congress declared yesterday that Soviet civil defense programs do not provide any reliable protection against U.S. strategic forces.

No rational Soviet leaders would risk starting a nuclear war, the Joint Committee on Defense Production said, because that war would inevitably distroy the Soviet Union as a great power.

The United States, the committee concluded, should not try to mimic or match the Soviet civil defense effort, because greater spending on civil defense here would prove ineffectual and a waste of money.

These conclusions appear in a 100-page report which amounts to a detailed rebuttal of alarms sounded the past year by some members of the strategic community concerned about the ongoing Soviet civil defense program. The committee majority said, in effect, that these alarms are unjustified.

Three members disagreed, and filed a minority report which said the Soviet program is menacing. However, they did not recommend a new American program to match it. They urged further study and analysis of what the Soviets are doing.

The civil defense issue has become heated in Congress. Last month the House voted to increase the civil defense budget from $90 million to $134.8 million, although the Carter administration did not want this extra money.

Proponents of the extra money said it was needed to prevent the Soviets from getting an advantage over the United States in civil defense.

The carter administration yesterday signaled its intention to spend less money on precautions against a nuclear war. In a change of policy, the administration will allow the states to spend federal civil defense funds to prepare for floods, hurricanes and other natural disasters.

This was announced by Bardyl Tlrana, new director of the Defense Civil Preparedness Agency in the Pentagon Tirana said communitis can use federal money for disaster planning provided they draw up plans for handling a nuclear attack. Previous regulations restricting use of federal funds to bomb shelters and other war preparations wasted money, Tirana said.

Tirana also said he could not use wisely any of the extra money the House appropriated for civil defense. "I do not seek it. I do not want it," he said.

In its analysis of civil defense, the Joint Committee on Defense Production made these points:

Soviet civil defense measures might be effective in protecting lives and industry against an attack by a secondary nuclear power like China or France, but there are no foreseeable circumstances in which they could give significant protection against an all-out U.S. attack.

The report analyzed the Soviet economy and concluded that it is too vulnerable to recover with any speed from a nuclear war. The Soviets' relatively undeveloped transportation network and its backward agriculture make it particularly vulnerable, the committee concluded.

Many crucial targets in the Soviet Union cannot be protected with the kinds of measures the Soviets use, such as building up walls of factories or digging shelters. Oil refineries were cited as an example of an unprotectable target.

The idea that the Soviets are building up their civil defense programs because they are contemplating a "war-winning" nuclear strategy does not make sense.

Those who view the Soviet program with alarm because it migh allow the Russians to survive a nuclear war with less damage than the United States take too narrow a view, the committee said. The question is not which superpower would suffer more, but whether either could remain a superpower after a nuclear exchange.

The committee said no reational leaders would launch a war unless they were confident their nation could survive with basic social political and economic institutions. This could not be assured with an foreseeible civil defense program, the committee said.

"To adopt the view that either nation can attain the ability to 'win' a major nuclear exchange in any meaningful sense of ther term or to survive it as a major power through passive industrial defense (i.e., civil defense measures) runs the risk of encouraging potentially dangerous stategic miscalculations," the committee said.

The committee is chaired by Sen. William Proxmire (D-Wisc.), hwo said in a press release that Soviet civil defense" and, therefore, do not need to be matched by this country.

The dissenting minority report which called for further study was signed by Sen. John Tower (R-Tex.) and Reps. Garry Brown (R-Mich.) and Chalmers Wylie (R-Ohio).

Washington Post staff writer George C. Wilson contributed to this story.