Unidentified thieves broke into the Harvard Athletic Department Ticket Office at 60 Boylston St. Sunday night, opened the safe, and escaped with the cash and checks inside.

Gordon Page, manager of the ticket office, said the exact amount of the loss would be determined in two or three days after taking an inventory. The safe never contained more than $500 in cash, he said, adding that the checks, made out to Harvard University, would be worthless to the robbers.

Robert Hallisey and Jesse Roderick, building superintendents, discovered the rifled office and open safe at 7 a.m. yesterday. They called the Harvard and Cambridge Police to investigate.

After inspecting the building, detective William Durette of the Cambridge Police described the burglary as a "professional assignment." Both Roderick and Page agreed.

The thieves entered the building by forcing a window in the basement and then broke through the inner door to the ticket office, Durette explained. Police are investigating a number of finger-prints found in the office.

The thieves also searched other offices in the building. According to Roderick, they tried to steal a piggy bank in an upstairs office, but, finding only 30 cents inside, left it up-turned.