Boeing Computer Services is close to withdrawing from its work on the federal government's mammoth FTS-2000 telecommunications system, following months of wrangling with its partner, American Telephone & Telegraph Co., industry sources reported yesterday.

Boeing has produced computer software as a subcontractor to AT&T, which is a co-operator of the multibillion-dollar FTS-2000. Spokesmen for the two said last night that the companies are talking about whether to extend the relationship into 1991. They said reports that Boeing has decided to back out are "premature."

AT&T spokesman Herb Linnen said that if Boeing does leave, the FTS-2000 system would not be disrupted because AT&T would do the work itself or find another subcontractor.

"We will deliver top-quality service and we'll get the job done to meet our commitments to the government," he said. "Boeing has not told us of a final decision to withdraw from the association. Our latest information was that they were going to take a look at what 1991 looked like ... and would come back to us."

FTS-2000, which links phone and communications systems in thousands of federal offices around the country, has been called the largest civilian contract since the Apollo moon program. AT&T runs 60 percent of the program; US Sprint Communications Co. has the other 40 percent.

By one account, Boeing employees were informed the relationship would end at a meeting at Boeing offices in Vienna yesterday. Boeing spokesman John Alter confirmed that there was a meeting but said he was unable to confirm or deny whether such an announcement had been made.

Boeing Computer Services is a subsidiary of aerospace giant Boeing Co. Its role in FTS-2000 has been to write computer software that runs the highly complex network. Over the course of its relationship with AT&T, it has had hundreds of people working on software at its Vienna offices, though the numbers are now much lower.

One industry analyst suggested that the impact of a Boeing departure would be minimized because the bulk of the software work has been completed.

For months, industry sources have said that the Boeing-AT&T relationship was not smooth. Boeing, it was said, had wanted a firmer contract than the year-to-year arrangement that AT&T offered.

Linnen, however, yesterday described the relationship as "businesslike and professional." Alter said he was not aware of a problem in the relationship.