Russian President Boris Yeltsin said he wouldtemporarily halt combat operations in Chechnyauntil the May 9-10 summit of world leaders in Moscow is over. Yeltsin's unilateral truce, which U.S. officials characterized as an effort todeflect attention from the civil war, came as the U.S. and Russia encountered new disagreements before President Clinton makes the trip. In Washington today, the State Department told Russian Foreign Minister Andrei Kozyrev that Russia cannot veto its former Eastern Bloc allies' absorption into NATO. And Russia, taking advantage of a U.N. promise to let Iraq sell $2 billion in oil, ruffled U.S. feathers by concluding an oil deal with Baghdad today. The State Department has already condemned Russia's $1 billion contract to help Iran develop a nuclear reactor complex near the Persian Gulf.