Office Technology Plus, the federal government's answer to the neighborhood computer store, formally opened for business yesterday with a ribbon-cutting robot and first-month sales figures that eclipsed all estimates.

Located on the ground floor of the General Services Administration headquarters, the outlet is designed to be a one-stop shopping place for federal employes who are authorized to buy desk-top business computers.

The GSA set up the store to provide not only the hardware, but the software, training and equipment maintenance that traditionally are unavailable when computers are purchased through the GSA's regular supply schedules.

The store is operated by a consortium of six suppliers headed by The Math Box Inc. of Rockville. Since opening Aug. 16, it has sold 135 computers and accessories, for a total of $1.03 million in sales. Under the GSA's contract with the operators, if the store earns more than $8 million in its first year, the contract must be renegotiated.

Despite GSA officials' prediction that the store would attract many employes who knew little about computers, Math Box executive Connie Fretwell said, "Most of our customers are intelligent, mid-level managers who have a good idea what they want."

Fourteen different computers are offered, at prices between 10 and 20 percent off the suggested retail price.