Britain's opposition Labor Party has a lead in the opinion polls for the first time since John Major replaced Margaret Thatcher as Conservative prime minister a month ago.

A poll in the Sunday Times gave Labor 45 percent, four points ahead of the Conservatives.Earlier polls since Thatcher's exit gave the government leads over Labor of two to 11 points. Labor had led for the last 18 months of her 111/2 year rule.

Major, who has inherited an economy hit by inflation and entering a recession, must call a general election by mid-1992.

Chancellor of the Exchequer Norman Lamont ruled out an early cut in high interest rates, now at 14 percent, which are depressing business activity and angering voters with mortgage repayments to make.

Lamont wrote in the Mail on Sunday newspaper that interest rates could not be cut if that meant easing up on anti-inflation policy and devaluing the pound sterling in the European Community currency grid.