NETANYAHU AGREES TO A CABINET POST IF A VOTE FOLLOWS
Former Prime Min Benjamin Netanyahu conditionally agrees to become Israel's foreign minister; says he will accept offer by Prime Min Ariel Sharon if government promises to call new elections soon and if he reaches understanding on three major issues; cites exile for Palestinian leader Yasir Arafat, which he favors, establishment of Palestinian state, which he opposes, and location of new fence along boundary of West Bank; he would replace Shimon Peres, architect of Oslo accords and supporter of two-state solution to conflict with Palestinians; offer by Sharon is latest move to recruit allies and box in rivals to shore up his minority coalition government now that Labor Party has dropped out; collapse of 19-month-old unity government in budget dispute and political implications of overture to rival Netanyahu discussed; photo (M),