THE CHIEF EXECUTIVE, having won office in a surprise victory, has instituted novel economic policies, cut back on the scope of government and pursued an assertive foreign policy. The results are generally disappointing: inflation is way down, but unemployment is at record high levels, and the promised economic growth from a liberated private sector has yet to occur. Yet the consensus is that the chief executive will win a second term in office for her party.

Yes, her: we're talking about Britain and Margaret Thatcher. Reagan boosters in the 1980 campaign liked to cite Mrs. Thatcher, who became prime minister in 1979, as a precedent. Later, as the British economy foundered and her popularity fell, one could hear from the White House that these two conservatives were actually following different policies. But if Mrs. Thatcher's Conservative Party wins a second term in the June 9 election, as predicted, talk about the similarities may again be in the air.

Working in favor of Mrs. Thatcher is the weakness of the opposition Labor Party. Its policies of unilateral nuclear disarmament, withdrawal from the Common Market and more state involvement in the economy are not popular, and few voters appear to see its leader, Michael Foot, as a strong prime minister. Its working class base, moreover, has been shrinking. Under stronger leaders, with more popular policies, the Labor Party since 1970 has won no more than 39 percent of the votes-- about what George McGovern won in 1972. Labor is getting about 34 percent in the polls now.

The outcome is not certain; the party of the prime minister who called three of the last four British elections has lost. And the British parliamentary system--so often ballyhooed as a panacea for our problems--allows a party with limited support and strong opposition to win and to govern, if the opposition is split. Currently that's not the case: Mrs. Thatcher's Conservatives are getting about 47 percent in the polls, while the Social Democratic- Liberal alliance has about 17 percent. But if the alliance, which led the polls in Britain before the Falklands War and has respected leaders, should gain votes, the race could tighten up.

So there are plenty of special circumstances to distinguish the British situation from the American. A Thatcher victory in 1983 is no guarantee of a Reagan victory in 1984. Moreover, though in Britain's 21/2-party system 47 percent of the vote is a landslide victory, in the United States in a two-candidate race it's a defeat. Still, a Thatcher victory, on the heels of the Christian Democratic victory in West Germany last March, would refute some part of the conventional wisdom that parties of the right cannot win in times of high unemployment.