An "ad hoc" group of Harvard and Radcliffe students will parade this afternoon to protest the recent bombings of North Vietnamese bases. Following a rally at 3 p.m. on the Cambridge common, the marchers will walk down Massachusetts Avenue to the Central Square Post Office and mail letters of protest President Johnson.

Today's rally is a prelude to a larger one planned for tomorrow. At that time, F. Stone, publisher of his own opinion magazine entitled "I F. Stone's Weekly" will address a crowd of "hopefully and maybe more," in Boston Common, Peter Orris '67, group spokesman said last night. The crowd will then march to Post Office Square and mail more letters to Johnson.

The rallies are part of a concerted effort "to protest the recent actions as acts of war, to end the war, and to cause the United States to withdraw from Vietnam," Orris said.