GAZA CITY, Gaza Strip — Israel and Gaza's ruling Hamas agreed Tuesday to an open-ended cease-fire after seven weeks of fighting — an uneasy deal that halts the deadliest war the sides have fought in years, with more than 2,200 killed, but puts off the most difficult issues. In the end, both sides settled for an ambiguous interim agreement in exchange for a period of calm. Hamas, though badly battered, remains in control of Gaza with part of its military arsenal intact.