Construction is proceeding ahead of schedule on new facilities in Palmdale, Calif., where Rockwell International will assemble 100 new B1B bombers ordered by the Air Force, a company spokesman said yesterday.

The contract calls for the first of the long-range combat planes to be delivered to the Air Force and enter flight tests in March 1985, but they could be early, he said. The first of the bombers, designed to replace the B-52s, now is expected to roll out of the assembly plant in October 1984 and to make its first flight test in December 1984, he noted. Deliveries of the first 15 planes are to be completed in 1986, with the 100th aircraft to be ready in early 1988.

The total cost of the B1B program is pegged at $20.5 billion in fiscal 1981 dollars by the Pentagon, although the General Accounting Office and the Congressional Budget Office think the cost will be considerably greater.

So far, Congress has appropriated $3.4 billion for the procurement of the first seven aircraft, including the high start-up costs of a production line, in fiscal 1983 and another $475 million for advanced procurement for aircraft in fiscal 1984, a Capitol Hill source said.

The controversial B1 program was canceled in 1977 by President Carter after Rockwell had built four of the aircraft. The program was resurrected by the Reagan administration, which gave Rockwell its production go-ahead last January.