The White House Council on Environmental Quality has decided to abolish a rule that requires federal agencies to consider the worst environmental consequences of their actions, contending that the regulation is "unproductive and ineffective."

The decision, to be announced today, caps a three-year Reagan administration effort to limit the reach of the National Environmental Policy Act (NEPA). According to the council, the amended regulations will improve the quality of environmental impact statements by establishing a "more careful and professional approach . . . in the face of incomplete or unavailable information."

The decision is likely to draw criticism from environmental groups, which contend that it reduces the government's responsibility when scientific and technological uncertainties play an increasingly large role in decisions affecting the environment.

Since 1970, NEPA has required federal agencies to prepare detailed analyses of the environmental effects of dams, nuclear waste disposal sites, pesticide-spraying programs and other federally financed projects.

The main target of the council's effort has been the so-called "worst-case scenario." Courts generally have upheld worst-case analysis as the best way to gauge the effects of events that are unlikely to happen but would be catastrophic if they did, such as a fully loaded supertanker sinking in Galveston Bay.

In its Federal Register notice, the council contends that such analyses "breed endless hypothesis and speculation." Agencies still will have to consider low-probability effects, it said, but only those that are "reasonably foreseeable" and supported by "credible scientific evidence."

"It does eliminate worst-case," said council Chairman A. Alan Hill. "Legitimate people will disagree that this is the best approach."

Hill said agencies will also have to disclose when there is insufficient information to gauge environmental effects. However, this requirement apparently applies only when the agency has decided that a significant adverse impact is "reasonably foreseeable."

National Wildlife Federation official Norman Dean said the change significantly weakens existing rules, which require agencies to disclose the absence of information in all instances. "The fact that information is missing in the first place makes it almost impossible to determine if a significant impact is reasonably foreseeable," he said.

"In the case of bio-engineered organisms being released into the environment, the old rule would have required a worst-case analysis. Under the new rule, an agency wouldn't even have to identify the fact that information is missing," Dean said.