In what was apparently not an attempt to keep up with the recent postal price increase, a group of local activists have increased the size of their letters.

More than 125 people signed a huge missive measuring four feet by thirty-six feet, addressed to Mikhail Gorbachev and drafted by Amnesty International, as they passed by Au Bon Pain in Harvard Square yesterday.

The letter was an appeal for the release of Hanna Mykhaylenko, a Soviet librarian from Odessa who was arrested in 1980 for advocating the right of Ukrainians to use their native language. She was declared insane and confined in a maximum security psychiatric hospital.

Martin Fuchs, coordinator for Amnesty International's Cambridge chapter, said the group plans to mail the huge letter directly to Gorbachev after collecting about 500 signatures.

The large size of the petition is designed to catch the eyes of passersby so that people beyond Amnesty's regular membership will get involved, Fuchs said.

He said that the Amnesty group in Cambridge has been working on Mykhaylenko's case for seven years. Fuchs said they have written thousands of letters about her. Their interest may have helped to prevent the Soviet government from administering powerful neuroleptic drugs--which he said are often given to Soviet psychiatric patients--to Mykhaylenko, he said.

Mykhaylenko was recently moved to a lighter security psychiatric hospital in her hometown, Fuchs said.

Daniel B. Nelson, a member of Amnesty International, said that letter-writing and petitioning are useful tools for dealing with totalitarian governments because "even dictators care about their PR. They want to appear as enlightened and as progressive as possible...It's good to call attention to their sins."

"If people keep bugging [Gorbachev] about this woman [Mykhaylenko] he might just release her," Nelson said.