For four months, Assistant Secretary of Energy Joseph J. Tribble has required his mail clerks to open and copy "any incoming correspondence" destined for a controversial subordinate division that has been the focus of close congressional scrutiny.

Some employes call the practice an unwarranted invasion of privacy. Others say it is common government practice.

A Feb. 7 memo by Tribble, the assistant secretary for conservation and renewable energy, directs that copies of correspondence to his section's Building Energy Research and Development (BERD) Office are to be forwarded to Tribble's special assistant, Norman Hughes.

The memo also gives two other Tribble aides the job of checking "correspondence related to the activity" of another three offices within the Conservation section--but not "any incoming correspondence."

Tribble was on vacation last week and not available for comment. Two top officials of the BERD office did not return telephone calls. But two other aides said the procedures are routine in government and that correspondence marked "Personal" or "Confidential" is not supposed to be opened.

On a few occasions, said Linda R. Gregory, director of Tribble's Office of Policy and Management, mail clerks unfamiliar with the procedure did open mail designated as personal. Gregory said that when she found out, she warned the clerks to be more careful.

"The intent was just to assure that the people on Joe's staff who should be informed as to what's going on were informed," said Tribble aide William Neustadt.

He added that similar procedures were in effect during the Carter administration, when Neustadt worked for the Energy Department's Office of Environment. However, the former head of that office, Ruth Clusen, and her special assistant, Carol Jolly, said no such procedures were in effect.

Gregory, a veteran of the Department of the Army and the Federal Energy Administration, also said that the mail-handling procedures are routine in government.

But Tina Hobson, a former career federal employe who is now appealing her recent dismissal as head of an office within BERD, said, "It's never been done as long as I've worked for the federal government . . . .

Hobson said that at times in the last two years--particularly during Tribble's frequent questioning by members of a House Energy and Commerce subcommittee--high officials in the energy conservation office cross-examined BERD employes to determine whether they gave information to the committee.

Congressional inquiries have focused on, among other things, Tribble's meeting with home appliance industry representatives while conservation standards for home appliances were being drafted. There were also hearings on the case of Maxine Savitz, a senior conservation official who was dismissed after she refused to move to Denver.

Regarding the mail-opening policy, one Energy Department source said: "Bureaucrats in general are used to a lot of wacky, weird-looking practices, but this causes a certain amount of unrest. You feel you're being watched."