Principal Joe Clark told a student body assembly at Eastside High, the school he runs with the assistance of a bullhorn and bat he carries through the corridors, that he will stop his verbal assaults on the Paterson, N.J., School Board. Earlier, Clark had said that two black school board members were "worthy of the guillotine" for failing to support him. Clark, who is also black, is facing disciplinary action by the board for an unauthorized suspension of 66 students he felt were malingerers. The assembly was held to announce details of an offer by Fort Lee businessman Jack M. Berdy and other officers of On-Line Software Internationl Inc. to donate $100,000 a year for 10 years to a scholarship fund for Eastside graduates studying computer science. The gift is conditioned on Clark's remaining principal or leaving Eastside only voluntarily.