For William D. Ruckelshaus, EPA administrator-designate, the honeymoon is already over. He hasn't even started his new job yet. But environmental groups have started to grumble loudly about the environmental positions Mr. Ruckelshaus took during his tenure as a vice-president of the Weyerhaeuser Corporation.
''Frankly, we are disturbed by elements of the past record of Mr. Ruckelshaus ,'' John McComb, the director of the Sierra Club's Washington office, told the Senate Committee on Environment and Public Works Tuesday.
The committee is holding three days of hearings on President Reagan's choice to replace Anne Burford as head of the EPA. Ruckelshaus himself will put in his first personal appearance before the committee today. Senate confirmation of the Ruckelshaus appointment is widely considered to be a foregone conclusion.
Appearing before the committee en masse, environmentalists still praise Ruckelshaus's managerial ability, and say they're impressed by his relative open-mindedness.
''A number of (environmentalists) have already had one or more meetings with Mr. Ruckelshaus,'' said William Butler of the National Audubon Society. ''His predecessor never accorded us a comparable opportunity.''
But they voiced concern, in particular, about the lobbying Ruckelshaus did for relaxation of the Clean Air Act while working at Weyerhaeuser.
A letter Ruckelshaus wrote to Vice-President George Bush in 1981 said that the Clean Air Act ''is a complicated, pervasive law that is causing our society to spend very large sums of money for marginal benefits.'' Ruckelshaus urged the administration to push for modification of the act.
In addition, Weyerhaeuser itself has dumped toxic wastes in at least three of the dirtiest waste sites in the nation, said Sidney Wolf, a lobbyist for Environmental Action. As head of the EPA, Ruckelshaus would be in charge of cleaning up that mess and possibly bringing suit against his former company to recover a share of cleanup costs.
Ruckelshaus's conflict-of-interest problems at EPA, Mr. Wolf warned, might therefore be ''unprecedented.''