Two investigators for the House ethics committee who were suspended last September were reinstated yesterday after an investigation cleared them of any improprieties, according to the committee's special counsel, Joseph A. Califano Jr.

Califano said in a prepared statement that the two investigators, John J. Moriarty and Richard J. Powers, who were working on the committee's probe of allegations of sex and drug abuse on Capitol Hill, were not involved in "any improper conduct in carrying out their duties."

"While there is evidence of human errors in judgment, the investigation clears both men of any impropriety," the statement said.

The statement yesterday and an earlier one made when they were suspended did not specify why they were suspended, or why the Justice Department also was investigating them.

Moriarty and Powers, in a joint statement yesterday, said they were pleased that the investigation cleared them, but added that they remained "puzzled and upset over this entire incident."

They said they were never told by Califano why they were under investigation or who had made allegations against them.

Sources familiar with the Justice Department investigation said one concern was a possible connection between the pair's work for the committee and work they had done earlier when they operated a private detective business.

Moriarty and Powers said in their statement that they looked forward to returning to their jobs with the committee.