For those who remember the Cuzco Caper - the story of the researchers who used federal grant money to study a Peruvian bordello - the National Institute for Mental Health has an after-word.

NIMH agrees that yes, maybe Sen. William Proxmire (D-Wis.) was right last week when he accused the agency of mismanaging the $97,000 grant.

And yes, NIMH agrees, maybe it should have kept better track of Pierre van den Berghe and George Primov and their investigation of ethnic and class relationships in the Peruvian Andes around Cuzco, seat of the old Inca empire.

But there the agreement ends. In no way, said David Pearl, chief of behavioral sciences research at NIMH, did the agency approve a brothel study.

Proxmire last week gave NIMH his Golden Fleece of the Month - a prize he bestows regularly for "the biggest, most ridiculous or most ironic waste of taxpayers- money."

After NIMH was awarded its Golden Fleece, Pearl acknowledged that the agency had some problems in monitoring the 18-month study. conducted in 1972 and 1973, and in obtaining final reports from the researchers.

But Pearl and van den Berghe, a professor at the University of Washingtion, said the brief study of the brothel was not included in the originalresearch proposal.

"We did not know about the study - it wasn't in the proposal nor in the progress reports," Pearl said. "If they had proposed it to us, I don't know if it would have been approved."

Van den Berghe said the brothel research by Primov, a University of Missouri professor, was done on his own time and cost no more than $50 in gasoline money form the grant.