Sen. William Proxmire (D-Wis.), looking for some statistics to support his suspicion that federal employes frequently tag their vacations onto government trips, asked the General Accounting Office to check how many bureaucrats take annual leave while away on official travel.

Back came the reply, over the signature of Comptroller General Charles A. Bowsher: Out of a voucher sample of 10,761 trips, submitted by 26 departments and agencies, employes took one or more days of annual leave while on government travel on 96 occasions. That works out to less than 1 percent. "On a weighted basis," Bowsher wrote, "we estimate that employes took leave on about 135,000 of the 12 million trips" government employes took in 1981, excluding relocation trips and home leave for overseas employes.

"It surprised us that it was so low," said Thomas L. van der Voort, an aide to Proxmire. Van der Voort said Proxmire had requested the check after learning of several instances of government employes saddlebagging vacation time onto government-paid trips to the West Coast and abroad.

Proxmire had attempted to stop the practice through an amendment to an appropriations bill, but it was knocked out in conference and replaced with conference report language requiring agencies to report quarterly to the Senate Appropriations Committee any official trips involving one or more days of annual leave.

Van der Voort said the requirement isn't legally enforceable and some agencies are antagonistic to it.