The U.S. is accepting bids for its phone system.

The General Services Administration formally opened the bidding for a 10-year contract to provide about 1.3 million federal workers with a new telecommunications system. Three major telephone companies have said they will bid on the contract, valued at more than $4 billion, and two or three other concerns are expected to submit bids as well. MCI has joined with Martin Marietta of Bethesda, Md., to try to secure the contract, while AT&T; and Boeing Computer Services of Seattle are teaming up.