The National Capital Planning Commission last week reaffirmed its decision against raising building height limits around Washington's historic Judiciary Square.

But the image of the square may be changed if the D.C. Zoning Commission, meeting today, ignores the federal planning agency and raises them anyway.

Besides opposing increased heights at Judiciary Square, the planning commission voted in favor of zoning changes to permit construction of a new French Chancery on Reservoir Road and approved revised plans for the $99 million downtown convention center, proposed at 9th and H streets NW.

The District government's proposed change in zoning to allow a 10-story, 120-foot commercial office building on Judiciary Square disregards its own seven-story, 90-foot height limit there as well as protests of both NCPC and the city's Joint Committee on Landmarks, the agency that protects historic buildings in Washington.

The 90-foot height limit, established in the city's 1971 master plan for Judiciary Square, is designed to keep high modern buildings from dwarfing the historic buildings around the square north of Pennsylvania Avenue at 5th, 6th, D and E streets NW.

Laid out in Pierre L'Enfant's 1791 plan for the Nation's Capital, the square includes among other buildings the original 1820 city hall and the unusual 1885 Pension Building, soon to become a national museum of the building arts. Metro's new headquarters and new federal buildings around the square all have been limited to 90 feet.

If the height limits are approved, however, the 10-story commercial office building soon would be followed by at least two other 120-foot office buildings on lots now vacant on the square, including one directly east of the Pension Building. The presently proposed building would occupy the site of the recently razed Georgetown University law school building, constructed in 1898.

The only reason given for changing the present special zoning around the square and permitting the height increases has been that developers want higher, more massive buildings because they will be more profitable. The zoning commission concluded as a "matter of fact" that not allowing developers to build larger buildings there will "effectively prevent development of this site," a "fact" disputed by planning commission members.

The zoning commission in December postponed a final decision on the issue until today, to give its staff and NCPC staff 60 days to see if they could reach a compromise.No agreement was reached on the crucial height issue, but while NCPC has reaffirmed its position against higher buildings on Judiciary Square, it also has suggested several ways 90-foot office buildings could be made larger to provide almost as much leasable space as 120-foot buildings.

Among the suggestions were those to permit a large rooftop "penthouse," perhaps with a restaurant, and to allow a building overhang above the second floor.

The square is one of several historic downtown areas zoned to protect small 19th century buildings against modern high-rise construction that would belittle them. The rest of Washington has a maximum building height limit of 130 feet, set in 1910 to preserve the skyline around the Nation's Capital, except for one low-lying section of Pennsylvania Avenue where 160-foot buildings are permitted.

The preliminary plans for the proposed downtown civic center approved by the planning commission are a scaled-down two-story version of the four-story center that NCPC objected to last January.

The commission praised changes that cut public parking from 750 to 375 spaces and preserved small areas of parkland originally proposed to be eliminated.

In recommending approval of zoning changes on Reservoir Road to permit construction of the new French Chancery, the commission commended the French government for new site plans that will have sufficient parking (617 enclosed spaces) to avoid parking problems on nearby streets. The plan will require cutting of only eight -- instead of 128 -- large trees on the eight-acre site, formerly part of the Archbold estate beside Glover-Archbold Park.

The new chancery will consolidate 400 French government employes now working in 11 offices around town. It is expected to be completed after 1982.