The Environmental Protection Agency is at a crossroads. With the nomination of William D. Ruckelshaus to become the EPA's new administrator, morale among career bureaucrats at the agency has taken an upward turn. Public expectations of greater attention to such matters as hazardous waste cleanup have been raised.
Environmentalists in and out of government are encouraged that Mr. Ruckelshaus appears to be the kind of person needed to lead a new protective effort on behalf of the nation's air, land, and water.
Few of them doubt there will be some major new EPA initiatives once Ruckelshaus is confirmed by the US Senate and is holding the agency's reins. One possibility: stepped-up attention to the most dangerous chemical waste sites on the federal Superfund cleanup list.
Also likely, environmentalists and EPA field directors say, is the assignment of additional investigators and attorneys to the agency's regional offices and perhaps even decentralization of the decisionmaking process on cleanup cases. Previously, agreements reached at the regional level on such cases had to be approved in Washington - a time-consuming and morale-sapping process.
''One of the things wrong with EPA was just plain incompetence,'' says John McComb, director of the Washington office of the Sierra Club. ''He (Ruckelshaus) is clearly going to turn that around.''
Paul Keough, acting deputy director of the New England region of EPA and a longtime colleague of the nominee, adds: ''Bill Ruckelshaus did not take a substantial cut in pay to come in and pussyfoot around. When he comes on, he's going to hit the street running.''
Ruckelshaus accepted the nomination on the condition that he have a free hand to name his own ''lieutenants'' and to recommend policy changes to President Reagan.
But as numerous critics of the Reagan administration have cautioned, there is a considerable difference between changing the captain of a ship and changing its course. They remain skeptical that even a person of Ruckelshaus's stature will make much of a difference to the environmental protection effort unless it is backed up by a change in philosophy on the part of the administration.
Some veteran environmentalists outside government also are unconvinced that Ruckelshaus, who won high praise as the EPA's first chief in the early 1970s, will bring exactly the same leadership to his job this time.
They are disturbed that he has the enthusiastic backing of Interior Secretary James Watt; that he has no guarantee his recommendations for policy change will be accepted by the administration; and that he says he does not want to make ''scapegoats'' out of businesses that pollute the water and air.
They also fret over Ruckelshaus's ties to firms that are either known polluters or are accused of improprieties in the cleanup of toxic waste sites.
Results of a Los Angeles Times poll released last week indicate that an overwhelming majority of respondents believe the Reagan administration has misused the $1.6 billion Superfund. Those polled also say they believe that the EPA has been making ''sweetheart'' deals with polluters to spare them some of the cost of cleaning up waste sites, and that this administration's environmental record is worse than those of its predecessors.
Thus, says a source close to the Senate Environment and Public Works Committee, which will consider the Ruckelshaus nomination, a confirmation will not be automatic.
Intensive hearings should be expected, this source says, because they will offer critics from both sides an opportunity to hold the administration's feet to the fire on the issue of environmental protection.
Senate committee chairman Robert T. Stafford (R) of Vermont won a tough reelection fight last November, in part due to environmentalist support. So did Sen. John H. Chafee (R) of Rhode Island, who also is leading the effort to reauthorize the Clean Water Act. Sen. George J. Mitchell (D) of Maine has introduced a tough anti-acid-rain amendment to the Clean Air Act, cosponsored by another minority member, Sen. Gary Hart (D) of Colorado.
The administration has not even sent the Ruckelshaus nomination to the Senate , and may not until political and news media criticism of the agency's prior course has cooled further. The hearings are not expected to begin until early May.
Once he is confirmed, however, some in the environmental community predict it won't be long before Ruckelshaus and Secretary Watt are opposing each other on key issues. And Watt still enjoys the unquestioned endorsement of the President.
Mr. McComb of the Sierra Club says there will be three early opportunities for the administration to demonstrate that it has had a change of heart on the environment:
* Hearings to reauthorize the Clean Water Act, already under way in the Senate and soon to open in the House. ''Although we're skeptical, this is very much an open book at this point,'' the Sierra Club leader says.
The administration has not yet introduced any legislation affecting the act, although acting EPA administrator Lee Verstandig says the agency has decided to support bipartisan bills that would keep most antipollution standards intact. For its part, industry admits to being on the defensive.
* Reauthorization of the Clean Air Act. One of the major concerns is acid rain, which the administration so far denies is a serious problem. Environmentalists say this approach will have to change before they take the administration seriously.
* Increasing the EPA budget. Ruckelshaus failed to impress a group of environmentalists last week when he did not promise to ask for a higher budget for the remainder of the current fiscal year. But there are suggestions that the White House may at least ask congressional approval to fatten the Superfund and extend the waste-site cleanup deadline past 1985.