President Reagan hailed a ''new chapter'' for the Environmental Protection Agency with this week's swearing-in of William Ruckelshaus as EPA administrator. It will be a stirring new chapter if all concerned follow through on the President's strong demands:
* That there be ''nothing less than full compliance with the letter and the spirit of the law.''
* That the agency ''operate in the sunlight so all can understand and participate in EPA's policy formation and decisions.''
Presidential leadership on such points speaks directly to those who praise Mr. Ruckelshaus's ability and integrity but warn that any appointee can be only as effective as the policies and commitment behind him at the top.
By stressing total compliance with the law, Mr. Reagan takes a step against repetition of EPA lapses that have drawn multiple congressional investigations. Questions have involved such matters as laxness, favoritism, and political manipulation in the enforcement of hazardous waste cleanup laws.
Congress is still watching. On the very day of the swearing in, the House voted 413-0 to cite former EPA official Rita Lavelle for contempt of Congress in refusing to testify before a subcommittee.
Evidently Miss Lavelle acted on her own. But when her former superior, Anne Burford, was cited for contempt, it was for withholding subpoenaed documents under White House orders. Later the administration made arrangements for congressional scrutiny of ttyhyo/ments, dra- izing how much time and turmoil could have been saved by open cooperation in the first place.
Now, by calling on the EPA to ''operate in the sunlight,'' Mr. Reagan rouses hopes for full public and congressional access to what is going on.
It might be noted that the President's own Council on Environmental Quality (CEQ), headed by A. Alan Hill, has been emphasizing the importance of openness and public participation in another part of the environmental protection process. This is the preparation of environmental impact statements as required in advance of various construction projects. The council has found not only that all parties then tend to be more comfortable with final decisions but that the decisions themselves are better.
The CEQ has a coordinating role in studies of acid rain. Some environmentalists think there has long been enough evidence for vigorous action against the industrial air pollution linked to acid rain. Mr. Reagan surprised some people when he avoided the administration's previous appearance of temporizing and urged Mr. Ruckelshaus to meet the acid rain issue ''head on.''
This assignment should be facilitated by budget increases for coping with acid rain and by a major scientific review of acid rain reports due this summer.
In short, the ''new chapter'' for the American environment could turn out to get rave reviews, especially with that author in the White House spurring all the other writers on.