Environmental Protection Agency Administrator William D. Ruckelshaus yesterday told a congressional subcommittee that the federal government "has a role" in protecting the nation's underground water resources, but that the primary responsibility should remain with the states.

"Ground-water protection has a very high priority at EPA," he said. "The problems we now face are the result of decades of misunderstanding and neglect of this vast resource."

But Ruckelshaus refused to commit the EPA to a federal policy for protecting ground water, despite gentle prodding from members of the House Government Operations subcommittee on environment, energy and natural resources.

Federal pollution-control laws require only "minor statutory adjustments" to address ground-water problems, he said, and these should await the recommendations of a task force that has been formed to study the problem.

Underground water supplies support most agriculture and industry and serve as the primary water source for more than 100 million Americans, according to EPA statistics. Ground water moves very slowly through underground reservoirs known as aquifers, making it susceptible to permanent contamination from hazardous substances seeping in from the ground above.

Rep. Mike Synar (D-Okla.), the subcommittee chairman, told Ruckelshaus it was "astounding" that the EPA has been unable to develop a coordinated national policy for protecting ground water.

"We are destroying significant portions of this essential resource through contamination and overuse," Synar said. More than 2,830 wells in 20 states have been contaminated in recent years from toxic wastes, pesticides, gasoline storage tanks and mining operations, he said.

Proponents of a strong federal policy on ground water expressed disappointment with Ruckelshaus' testimony.

Rep. Dennis E. Eckart (D-Ohio), testifying in support of proposed legislation to strengthen the federal role in protecting underground water supplies, criticized the slow progress the EPA has made on the issue.

"A task force is fine," he said. "But action would be even better."

The task force is one of 10 that Ruckelshaus has created to analyze current problems facing the agency. It is expected to finish its report by this fall.

"Environmental protection--when left to the states--has historically led to inadequate and sporadic protection," said Daniel Weiss, a water specialist with the Izaak Walton League. "Aquifers know no legislative or legal boundaries. Uniform standards, applied nationwide, are the only way ground-water protection can be effective."

A recent Congressional Research Service report comparing the ground-water-protection proposals of the Carter and Reagan administrations said the Carter version presumed that a high priority should be given to drinkable ground water. But the Reagan policy, it said, "speaks only to the need for a better understanding of ground-water contamination . . . ."