Part of the Yard remained closed to traffic for an hour yesterday as police and fire officials investigated a suspicious unmarked package delivered to Wadsworth House.

Following Harvard's new stringent mail bomb precautions, the Cambridge Fire Department, Cambridge Police and the Boston Police Bomb Squad all responded to what was later discovered to be only an improperly addressed letter.

"We couldn't identify where it came from. It had no return address...only Wadsworth Hall," said one Wadsworth employee, who asked to remain anonymous.

Consequently, Harvard police were called in to ascertain the contents of the package but could not do so without proper x-ray equipment, according to Lt. John F. Rooney. Police then alerted bomb squad technicians.

The southwest corner of the Yard was sealed off while bomb squad officers performed an on-the-scene x-ray of the package. After determining that the unmarked package was harmless, officials re-opened the Yard to normal traffic. Rooney called the police action "a simple procedure" performed "to err on the side of safety."

Harvard employers were warned to follow more stringent security measures this year after two mail bombings occurred this summer at other universities. The F.B.I. warned that the absence of a return address is a possible sign of a mail bomb.

"This is still considered a big issue," said Lt. Murphy of the Harvard Police Department.