Washington — President Reagan toured a cave, visited a Potomac River island, and petted a baby bald eagle last week on a whirlwind tour of the great outdoors designed to portray the President as a friend of the environment.
According to one high administration official, the trip shows the White House has had a real change of heart since the days of James G. Watt, the controversial former Interior secretary.
''What we're seeing is a president being responsive to publicly expressed concerns,'' says William D. Ruckelshaus, administrator of the Environmental Protection Agency (EPA). ''That's the way the system is supposed to work, isn't it?''
Speaking at a breakfast for reporters, Mr. Ruckelshaus insisted that Mr. Reagan really is concerned about nature. But the EPA chief says his boss's environmental instincts are of the old-school, let's-save-a-tree variety.
Reagan's ''understanding of the environment is more that of a traditional conservationist than of someone attuned to the toxic-waste problem that has exploded on us in the last few years,'' Ruckelshaus admits.
Environmentalists, of course, describe the President's environmental attitudes in much less charitable terms. One environmental group offical grumbles that Reagan's outdoor experiences of last week were ''sun, fluff, and rhetoric.''
But most environmentalists, when the subject turns to Ruckelshaus himself, will either fall silent or say guardedly positive things. The tall, exuberant head of the EPA is widely seen as a moderate man in a tough position.
Ruckelshaus was the EPA's first administrator, back in the early 1970s. Among other things, he has been deputy attorney general (he refused to fire Watergate special prosecutor Archibald Cox, and was thus one of the officials dispatched in Richard Nixon's ''Saturday night massacre'') and a high official of the Weyerhaeuser Corporation.
When asked about his predecessor at the EPA, Anne Burford, Ruckelshaus will say only that the approach to environmental problems first taken by the administration was full of mistakes. ''I feel very good about the way the agency is now running,'' he says.
''At the beginning of this administration, lots of industry people thought they had the upper hand'' on the environment. ''That was stopped dead in its tracks.''
Today, he says, some momentum is swinging back to the environmentalists, and they are gaining some advantage on such issues as the Clean Air Act and the toxic-waste cleanup Superfund.
During Ruckelshaus' first stint at EPA, his problem was controlling pollutants you could ''smell, touch, and feel,'' he says. But now the US is running into a ''second wave'' of environmental problems, such as toxic-waste dumps. ''They're a lot more complicated and a lot less clear,'' he says.
Last year, Ruckelshaus, within the administration, championed a cleanup program aimed at suspected sources of acid rain. He was overruled by other officials, who stressed high cost and scientific uncertainty.
Ruckelshaus points out that even if the administration wholeheartedly backed an acid-rain bill, Congress is deeply split on the issue. He doubts a ''sensible'' program could be passed.
''It's a sectional problem'' on Capitol Hill, he says, pitting Midwesterners against Easterners.
Today, much of the acid-rain debate centers on its effect on lakes, but Ruckelshaus predicts that a growing realization of its ''effect on forests will ultimately drive a solution.''