Ronald Reagan's friends are running very well in Europe these days. Helmut Kohl led the Christian Democrats to victory in West Germany in March, and all the polls predict that Margaret Thatcher's Conservative Party will be returned to power with an enhanced majority in Britain's election tomorrow.

That means strengthened support for the Western alliance policy (which predated the current governments) of deploying cruise and Pershing II missiles in Western Europe later this year even as the arms control talks with the Soviet Union continue at their wearying pace.

It also means that in the United States, Germany and Britain there are governments in power that support liberal trade policies, lower taxes and a broad effort to slow the growth of the public sector, even at the cost of higher unemployment and more limited social services.

Pattern-finding is not predestination, of course, but it is impossible not to find some parallels in the politics of these three closely linked nations. One of the most striking is the bankruptcy of the parties of the left that until recently provided leadership for all three countries.

The Social Democrats in Germany won 38 percent of the vote in March, their lowest figure since 1961. The Labor Party, according to pre-election polls, may win less than one-third of the vote here in what could be its worst showing since 1931.

This comes after the Democratic Party in the United States slumped to 41 percent of the vote in 1980, its second-lowest figure since 1928.

Part of the explanation surely lies in the massive wave of inflation that struck the industrial countries in the 1970s, when the OPEC nations pushed up the price of oil. The governments of Jimmy Carter, James Callaghan and Helmut Schmidt were the victims of that inflation as much as they were of any shortcomings of their own. Inflation creates anxiety to preserve what a family already has achieved; conservative politicians can appeal to that fear of loss.

There was a particularly striking evidence of that appeal in a poll taken during the final week of the British election campaign. Voters were asked what they expected would happen if Thatcher and the Tories were given another turn in power. Large majorities said the Tories would not reduce unemployment, would not cut taxes and would not improve living standards. Large majorities said the Tories would cut welfare state services and make the rich richer and the poor poorer.

That sounds like a prescription for political ruin. But the poll found that the highest single percentage--66 percent--believed that the conservatives would keep inflation down. And that belief apparently outweighed all the others.

The other side of the story is what has happened to the parties of the left in terms of their own leadership and policy. There is a widespread view here --again, supported by the polls--that as many people are voting against Labor's leaders and programs as are voting for the Conservatives.

Since its defeat in 1979, the Labor Party has lost its grip on reality and has moved into a fatal embrace of unilateral disarmament, withdrawal from the European Community and further nationalization of industry. The voters are not buying it.

Because they are not, and because the British election system makes it almost impossible for the third-force Alliance of Liberals and Social Democrats to win very many seats in Parliament, Thatcher can come out of this election as the single strongest leader in the NATO countries.

That is very good news for Reagan-and a very strong warning to his domestic opponents not to underestimate his electoral strength going into 1984. The Tory campaign is a version of Reagan's midterm election slogan, "Stay the course." The Conservative billboards here read: "It's starting to work. Don't turn back."

Knowing what happened in Germany and watching what is happening here, it is hard not to feel that "there is a tide in the affairs of men" and, at the moment, that tide is pulling many countries and many electorates in a conservative direction.

Not joyfully, perhaps. And not eagerly. Not with a sense that it's likely to produce quick miracles or even necessarily a better living for individual voters.

But I have heard the same things said by British voters this week that I heard two weeks ago in grass-roots interviews with voters in hard-hit Rockford, Ill. They are not blaming the conservatives in power for causing unemployment. They are crediting them with curbing inflation. And they are looking skeptically at the alternatives coming from politicians of the left.