U.S. AND RUSSIANS AGREE TO PUT OFF DEADLINE ON ARMS
US signs package of arms control agreements intended to break logjam that has stalled ratification of Start 2 in Russia, and among them are an agreement giving Russia another five years--until end of 1997--to dismantle launching systems; launching systems must still be disabled by 2003, and Clinton Administration say new agreements, which include Kazakstan, Belarus and Ukraine as well as Russia, will clear the way for new talks to negotiate further cuts in nuclear weapons in Russia and US; another accord modifies Anti-Ballistic Missile Treaty of 1972, reaffirming prohibition on longer-range defensive weapons and barring US from testing or deploying any spaced-based missile defense system but providing new flexibility for development of shorter-range systems intended to replace weapons like Patriot missiles used in Persian Gulf war; graph (M)