Claus von Bulow has agreed to divorce his comatose spouse and renounce his claims to her fortune, a lawyer for his stepchildren said. Von Bulow agreed also to give up a $120,000-a-year trust fund she set up for him before lapsing into a coma on Dec. 27, 1980, attorney Michael Armstrong said. Von Bulow, 61, was convicted in a first trial, but acquitted after a second trial in 1985 of charges that he tried to kill his wife, Martha (Sunny) von Bulow, 56. Her fortune is estimated at $50 million. A month after Von Bulow was cleared of criminal charges, the two children of Mrs. Von Bulow's first marriage--Alexander von Auersperg and Annie Laurie von Auersperg Kneissl--filed a $56-million civil suit against their stepfather in U.S. District Court in Manhattan, claiming he tried to kill their mother with insulin injections.