Systems Center Inc., the Reston-based computer software company, yesterday announced it would fire 92 of its 800 employees and post a major one-time loss in connection with software acquisitions made in the past year.

The company, which had revenue of about $100 million last year, said it would post a special one-time loss of at least $25 million in the fourth quarter after a year marked by numerous acquisitions and management shake-ups. About 30 of those to be dismissed work in the Washington area, Systems Center said.

Although the software company refused to link the layoffs to any one incident, it was hit hardest after paying $86 million for ownership and marketing rights to Netmaster, a network management system that links computers through software.

After trading as high as nearly $25 a share in the past year, Systems Center stock closed yesterday at $4.87 1/2, down 12 1/2 cents.

"This has been a turbulent year," said Rich Moore, vice president of the company. "We don't try to hide that fact."

Moore said the company would lay off employees at all levels in its offices in the United States, Europe and Japan.

At the same time, Moore said new senior executives would be added in finance, product engineering and sales. Robert Cook continues as chairman and chief executive officer.

"Our business continues to evolve," Moore said. "That means reallocation of resources... . We're not saying that just because we had layoffs that we're not going to continue to hire" in other positions.

Systems Center said that it expects to report revenue of $35 million and net income of $1.2 million to $1.8 million (12 to 18 cents a share) in the fourth quarter of 1990, not including the $25 million one-time loss due primarily to the Netmaster software acquisition.

In the fourth quarter of 1989, Systems Center reported revenue of $26.8 million and net income of $5.7 million (55 cents). In the first nine months of 1990, Systems Center reported a loss of $2.7 million.

James C. Mendelsohn, an analyst with Morgan, Stanley & Co. in New York, said the company had shown "some evidence of problems in the last month" and had turned in an erratic performance during the past year.

The company experienced drastic change last summer.

In June, Systems Center completed the purchase of Software Developments International, an Australian manufacturer of the Netmaster software. It paid about $43 million to buy the company, three months after paying about the same amount to buy Netmaster's worldwide marketing rights from another firm, Cincom Systems of Cincinnati.

Because it had to assimilate about 225 new employees after buying theAustralian company, Systems Center took a second-quarter loss of about $5 million. Its stock price dropped then, and John Barry resigned as president of the company.

Still, Moore said Systems Center continues to believe that the investment in Netmaster was a good one. Last summer, Cook said that the purchase would make Systems Center No. 2 in the rapidly expanding networking market, behind International Business Machines Corp.

"It's the hottest market in the world right now," Moore said.