Federal and state governments took legally required enforcement action for only 2.6 percent of more than 100,000 violations of the Safe Drinking Water Act in fiscal 1987, a conservation group said Thursday.

It is the policy of the Environmental Protection Agency to permit 23 months to lapse before even considering enforcement actions such as fines, lawsuits or administrative orders, the National Wildlife Federation said in releasing its findings.The federation said the nation's water systems or states notified customers of only 6 percent of the violations instead of every single one as the law requires.

The federation said it examined 15,000 pages of EPA records covering the 1987 fiscal year and found that 36,763 public water systems committed 101,588 violations of the act. The affected water systems serve about 40 million people.

Peter Cook, deputy director of EPA's Office of Drinking Water, said he was at a loss to explain how the federation arrived at its figures. He said his office recorded about 2,800 systems with "significant" violations in 1987, and 15,500 systems with violations EPA believed minor, a decline from 4,500 and 17,000, respectively, the year before.

"All regulatory agencies must have enforcement discretion," Cook said. When EPA finds a violation, "It is our position that it need not be an enforcement action" that follows.

Sixty-four percent of water systems serve fewer than 500 people, with 73 percent of significant violators and 83 percent of minor violators that small or smaller, Cook said.

Small systems may have difficulty raising money for the best equipment, he said. "It may take some time for this community to float a loan. . . . You're talking about years. It doesn't make a lot of sense, if you have a cooperative community which is moving ahead, to beat them over the head with penalties that they can't afford anyway."

Communities may be fined up to $25,000 for each day of violation, though fines that large are rare.

In Utah, 313 violations were reported during fiscal 1987, and there were 518 violations in the state's 934 systems. There were no federal or state enforcement actions.