The face has changed at the Department of the Interior, but will the song remain the same? William P. Clark, President Reagan's new nominee for the Cabinet seat, at least represents a switch in styles. Judge Clark is genial and low-key; his predecessor, James Watt, at times didn't seem happy unless breakfast came with a side order of controversy.
But Clark's appointment is not a clear sign that the administration is softening on environmental issues, as was the installation of William D. Ruckelshaus to head the Environmental Protection Agency, most analysts here explain. It's unlikely, they say, that Clark will substantially alter Watt's policies.
''I don't think a lot is going to change (at Interior), though things will be much quieter over there,'' says an aide to a Senate Republican who serves on the Energy and Natural Resources Committee.
Judge Clark's prime qualification for his new post appears to be the fact that he is one of Ronald Reagan's most trusted aides. He has little experience with environmental or energy issues.
As a stalwart Western conservative, however, Judge Clark likely shares Mr. Watt's pro-development view of natural resources, say Republican sources. During his 1973-81 stint on the California Supreme Court, Clark was the least ''preservation-oriented'' justice, according to a UCLA Law Review survey.
And in any case, Watt's influence will linger at Interior even after the new secretary takes his post. A skilled bureaucrat, Watt during his tenure stocked dozens of key lower-level posts with loyal followers. ''They're the ones running the department,'' claims Tim Mahoney, a Sierra Club public-lands specialist.
Though Clark's calm nature could help ease the now-strained relations between Interior and Congress, it may take more than a change in style to mollify Capitol Hill. Irritated with Jim Watt, and with one eye on the '84 elections, Congress is increasingly taking natural-resource policy into its own hands.