The General Services Administration must prepare a detailed analysis of the environmental consequences of its use of a controversial, partially occupied private office building at Buzzard Point in southwest Washington for government office space, a federal judge ruled here yesterday.

U.S. District Judge Louis F. Oberdorfer said preparation of the statement could lead to the possible use of shuttle buses to provide transportation between the isolated building and a subway stop; possible orders that GSA provide additional security measures in the area, and the implementation of parking regulations that might induce commuters to use public transportation instead of private automobiles.

In the meantime, Oberdorfer said the government must give 30 days' notice if it increases the number of employees in the building above the 800 now working there. The building could hold as many as 2,300 workers.

Oberdorfer was sharply critical of the manner in which GSA decided more than a year ago that the environmental consequences of its ease on the building were too minor to warrant a detailed impact statement. He said the GSA assessment discussed such items as general weather conditions in Washington instead of specific environmental issues in the Buzzard Point area.

The assessment by GSA was "very limited, often conclusory and . . . clearly inadequate," Oberdorfer said in a written opinion, which lawyers in the case said could have a wide-ranging impact on the manner in which the govenment leases office-building space for its hundreds of thousands of employees here.

The judge said, for example, in the field of automobile pollution that the GSA assessment did not reflect "any GSA sense of serious responsibility for facilitating subway use and reducing private automobile use by government-employed commuters."

Neither did GSA's environmental assessment include the safety threat to children in the area from the increased automobile traffic, nor the possibility that the government might abandon its use of the building when the GSA lease ends in 1981, Oberdorfer added.

Oberdorfer's ruling came in a suit brought by several local community-housing groups protesting use of the building. The groups, represented by attorney Fred Miller, contended that GSA should have prepared an environmental impact statement before agreeing to lease the building because the occupancy of the building will have a significantly impact upon traffic, air quality and other elements of the relevant environment.

The government originally intended to lease the space in the building to house part of the Securities and Exchange Commission, which was looking for a new home. The firm that constructed the building did so after receiving a ease commitment from the government.

SEC successfully opposed its assignment to the building, and the GSA was unsuccessful in its attempts to move many other government agencies there. Most government employees bluntly said they opposed moving there because of the building's isolation, lack of public transportation, and security problems.

Agencies housed there now include the Washington field office of the FBI, the Civil Service Commission, the Air Force Department, the Army Surgeon General's Office, and the Air Force Advocate General's Office.

Before accepting the lease, the GSA wrote a 93-page environmental assessment that it said took two days to prepare. It acknowledged many of the site's faults, Oberdorfer noted, but concluded only that "there will be some unavoidable congestion and additional air pollution during peak hours of traffic."

Oberdorfer said the government's role in the occupancy of the nine-story building amounted to a "major federal action" and was therefore subject to more detailed environmental treatment.

Such a detailed analysis, he pointed out, should have included alternative sites, possibly some nearer the city's costly subway system.

He rejected the GSA's argument that the case was moot since the building already is completed, saying the GSA actions in connection with occupying the building "have continuing impact at every weekday rush hour. It is plainly within the power of the court to enjoin any continuing nuisance or even less notorious government-related environmental impacts . . ."