United Press International yesterday filed for protection under Chapter 11 of the federal bankruptcy code, saying it must reorganize after compiling $45 million in liabilities against an estimated $20 million in assets.

The news agency said it had listed about 1,500 creditors in papers filed with the U.S. Bankruptcy Court for the District of Columbia.

Francis DiCello, a Washington attorney, filed the court papers at 5:45 p.m. UPI quoted him as saying, "Basically, what happens in a Chapter 11 is the filing of a petition allows some breathing space for the corporation to restructure its affairs."

David Wickenden, a UPI spokesman, told the Associated Press that, effective yesterday, UPI raised rates for its clients by 9.9 percent, a move he said was aimed at generating several million dollars in additional revenue.

UPI's four-member board of directors authorized the filing Friday after the agency was unable to cover its April 26 payroll.

The filing would stop creditors "from taking any enforced collection action pending further order of the bankruptcy court," DiCello said.

According to UPI, the court will be asked to grant permission for UPI to cover last week's paychecks for nearly 2,000 employes, who were advised Thursday night that their checks would bounce if deposited.

The court also will be asked by UPI to approve payment of four weeks' pay to about 80 employes laid off without notice Friday.