Chances that Prime Minister John Major may call for an early election are improving. With his Mar. 19 budget, Major cut former Prime Minister Margaret Thatcher's unpopular poll tax by one-third. Major's budget also would limit tax relief on mortgages for high-income earners, a populist gesture that may play well with ordinary Brits. If the ruling Conservative Party makes a strong showing in May 2 local elections, the betting is that Major may call a general election as early as June. But with the Tories and the opposition Labor Party now neck and neck in the polls, some advisers counsel a delay.