Car Bomb Kills 2 Israelis and Threatens Truce Effort
Car bomb kills two Israelis after it explodes near open-air market in Jerusalem, threatening early morning truce agreement between Israel and Palestinians; bombers flee on foot; site of bomb has been favorite target of Islamic groups during previous waves of terrorism; despite cease-fire pact, Palestinian gunmen open fire once more on Gilo, southeastern Jerusalem neighborhood, and Israeli troops return machine-gun fire toward shooting in Palestinian town of Beit Jala; 17-year-old Palestinian is shot dead in clash in village of Hizme near Jerusalem; Prime Min Ehud Barak of Israel calls Yasir Arafat, Palestinian leader, to express consolences; death toll from monthlong conflict rises to 168; photos; map (M)