The Board of Zoning Appeals voted last night to prohibit a Duncan' Donuts from opening shop in Harvard Square.

The four-to-one decision approved the appeal of the Harvard Square Defense Fund, a citizen group which argued hearing two weeks ago that bakery owner Duarte Carvalho should have to apply for a special permit in order to set up a fast food operation in Harvard Square.

Carvalho's attorney Edward J. O'Connell said he was "disappointed" by the board's decision. He said his client has still not decided whether he will appeal the decision.

Under city law, fast-order food business are prohibited in the square unless the owner receives a special permit from the Board of Zoning Appeals. The owner of The Country's Best Yogurt applied for and received the permit, and passed it on to Carvalho when he leased the space earlier this year.

O'Connell insisted in the hearings that the permit shooed continue to apply because Carvalho's Dunkin' Donuts would serve approximately the same fare as the yogurt store.

"They're making a distinction between two types of use that the ordinance doesn't recognize," he said of the board's decision to revoke the permit.

At earlier hearings Gladys P. Gifford, president of the defense fund, called O'Connell's argument an "ingenious way to get around applying for a permit by piggybacking on the old one ."

The fund insisted that Carvalho apply for his own permit, and appealed to the board to revoke permit.