The Boston Redevelopment Authority (BRA) yesterday removed one of the main obstacles to the construction of Harvard's $109 million Medical Area power plant when it voted to approve a set of revisions in the plant's design.

The State Department of Environmental Quality Engineering must still approve the plans for their expected impact on air quality in the area. The department's decision is expected to come by the end of next week, after which the public will have 30 days to comment before the decision becomes final.

The BRA board on September 29 asked its attorney to draw up a statement approving the plan revisions, and it approved that statement yesterday.

The project, entitled the "Medical Area Total Energy Plant," is designed to provide steam, chilled water and electricity to the Medical School, four Harvard-affiliated teaching hospitals, and other institutions in that area of Boston.

The BRA board originally approved the project in October 1975, but considerations of reliability and air quality control have since caused Harvard to hire a new engineering firm to redesign the plant.

Amendments to the original project plans forced the BRA to reconsider the plans. The BRA to responsible for granting zoning code and city noise code exemptions.

The plant is expected to exceed area noise standards at night even though, according to a statement adopted by the BRA board yesterday, the project includes noise control devices costing a total of $5 million.

The BRA decision includes the stipulation that members of the Medical Area Service Corporation--Harvard helath schools and affiliated hospitals--must "agree to take and pay for sufficient electrical power from the project so as not, in the reasonable opinion of the authority, to affect the feasibility of the project."

At the board meeting last week Robert L. Farrel, chairman of the board, said none of the member institutions had yet agreed to take power from the project.

The project as amended would include nine generators with an expected total capacity of more than 74,000 kilowatts, and underground fuel storage tanks with a capacity of more than one mission gallons.

Although project completion waits on approval from the state environmental quality department, work on the foundation is already we 1 underway with a building permit from the City of Boston