The National Wildlife Federation yesterday urged a Senate committee to approve William D. Ruckelshaus as administrator of the Environmental Protection Agency, calling him "a known quantity" whose experience is needed to restore credibility to the battered agency.

Four other environmental groups, testifying before the Senate Environment and Public Works Committee in the first of a planned three days of hearings, offered no opposition to Ruckelshaus, but declined to endorse him.

"We take no position ourselves," said Richard E. Ayres, senior attorney for the Natural Resources Defense Council (NRDC). "We think it's important to permit him to clarify his statements." Ruckelshaus, who did not attend yesterday's hearing, is to testify today and Thursday.

Of particular concern to the environmentalists are the opinions Ruckelshaus has expressed as a senior vice president of the Weyerhaeuser Co., a forest products firm that Environmental Action listed in 1981 as one of the nation's five worst polluters.

In a series of letters obtained by the committee, Ruckelshaus attacked the Clean Air Act and other environmental laws as overly stringent and expensive, and pressed for regulatory strategies that would weigh the cost of a government rule against its potential benefits.

John A. McComb, Washington director of the Sierra Club, said Ruckelshaus' statements reflect the attitude of his predecessor, Anne M. Burford, who resigned March 9 amid wide-ranging allegations of mismanagement and political manipulation of the agency.

"Will Mr. Ruckelshaus' 'regulatory relief' differ from Mrs. Burford's 'relief' only in that it is not outright illegal?" McComb asked.

Sidney Wolf of Environmental Action, the most skeptical of the groups testifying yesterday, told the panel that Ruckelshaus "bears watching" because of his long association with Weyerhaeuser.

"It would be Pollyannaish not to think that a major reason President Reagan nominated Mr. Ruckelshaus was for a favorable public image, much the same reason Weyerhaeuser hired him," Wolf said.

But Jay D. Hair, executive vice president of the wildlife federation, said the EPA "is crippled and it needs help, not confrontation." While he said that the group's support of Ruckelshaus is "not an endorsement of Reagan administration policies," he added, "We believe it's time to get back to business, and we believe Ruckelshaus is the person to do that."

In pointed and sometimes testy questioning, Sen. John H. Chafee (R-R.I.) pressed the environmentalists to explain their opposition to negotiated settlements under the "Superfund" hazardous-waste cleanup law, some of which have been criticized by environmentalists and congressional critics of the EPA as "sweetheart" deals favoring industry.

William Butler, vice president of the National Audubon Society, responded that the settlements were "closed-door" agreements that must involve "more interested parties than industry and the EPA" and must be available to the public.

"You would not consider that the EPA represents the public?" Chafee asked.

"No," Butler replied.

But he added that he expected Ruckelshaus to be more open than Burford in negotiating contracts to clean up hazardous-waste dumps. "If he has a strong point, it is that he is in favor of open covenants, openly arrived at," Butler said.

The NRDC also urged the panel to seek a commitment from Office of Management and Budget Director David A. Stockman that the EPA would be exempt from a presidential directive giving the budget office the power to review and reject regulations.

"Moving the fox out of the henhouse does little good if the fox retains the key to the farmer's shotgun cabinet," Ayres said.

While Ruckelshaus is expected to face extensive questioning on his record, some of the witnesses yesterday suggested that they did not expect to be satisfied by his answers.

McComb said the Sierra Club would reserve "final judgment until after some years of performance."

Sen. George J. Mitchell (D-Maine) responded, "It's all well and good to say you've got to wait and see how he does in office, but we don't have that luxury. We can't wait two years.

"Who in this country is going to say, 'Appoint me to this position and I'm going to carry out the laws except the ones I don't believe in?' " Mitchell asked