One of only two remaining bidders for a proposed $4.5 billion federal telecommunications network said yesterday that it would pull out of the competition if the contract is split up, as suggested by the chairman of the House Government Operations Committee.

"Our position is that if the contract is changed to a two-vendor selection or is in any way changed ... . then the Martin Marietta team will be withdrawing," said Jerry Thames, vice president for communications systems at Martin Marietta Corp.

Rep. Jack Brooks (D-Tex.) late Tuesday sent Martin Marietta a copy of a letter he had written to Terence C. Golden, head of the General Services Administration, expressing concerns about awarding the contract to a single vendor. GSA is handling the procurement, one of the largest ever, and bids are due Aug. 31.

"I strongly believe that the procurement should be restructured to allow for a multivendor award with continuing competition throughout the life of the contract," Brooks said.

Meanwhile, a spokesman for the American Telephone & Telegraph Co., leader of the other team bidding on the contract, said, "We think Brooks' view is reasonable."

"As far as AT&T is concerned, the chairman {Brooks} has raised some reasonable concerns about the contract," said A.J. (Herb) Linnen, the company's spokesman in Washington. "We have competition now as a fact of life, we are used to it and we feel we can be very successful in a competitive situation.

"Right now we're driving hard to meet the only proposal out there," he said. "But if in the final analysis the government makes a different judgment, we're not locked into any one approach."

A Martin Marietta spokesman said that AT&T "is drawing down several million a month in revenue" from providing much of the government's current service, and feels "no pain" from delay.

"There are procedures to draw this out ad infinitum," said Thames. The costs of preparing a bid have been in the "tens of millions of dollars over the last two years."

Federal officials -- who are counting on the system, known as FTS-2000, to replace the government's current costly and outdated network -- say they fear the whole procurement process is at risk.

At issue is the largest proposed telecommunications network in the world. It is supposed to deliver voice, data and video services to federal agencies by the 1990s.

One official described the current situation as one in which Brooks and Golden have each drawn a line in the sand, and the one with more key players lined up behind him by the end of the week may force the other to yield.

Brooks said in his letter to Golden that he thought the current "two bidder situation" was already unlikely to meet the requirements for a competitive contract.

In addition to AT&T and Martin Marietta, a third consortium made up of US Sprint Communications Co. and Electronic Data Systems Corp. once planned to bid but withdrew last month. Sprint is known to be interested in reentering the fray.

Brooks said in his letter to Golden, "I recognize that after two years of working on this project, it is difficult for you and your staff to be faced with the problem of having to restructure this procurement. However, I believe a multivendor award with continuing competition throughout the life of the contract will greatly reduce the risks inherent in the project and will ensure that the future telecommunications needs of the government are met economically and efficiently."

Golden has adamantly backed the winner-take-all approach, which he says will save money and time and would create fewer problems in changing from the current system to a new one.

"The most important aspect of this procurement is that it gets the government beyond the transition period," Golden said in a written response to Brooks. "The transition is extremely complicated to manage and will require careful and detailed management."

The federal telephone system "serves 78 government agencies, with about 1.3 million telephones, 11 million transmission miles and roughly 1,655 local switchboards," Golden said in his letter, adding that getting off the old system and onto one using new and different technology is difficult when "continuity of service is essential.