Transatlantic politics takes some funny turns. On the very day that Michael Foot, Britain's Mr. Disarmament, was stepping down after leading the Labor Party to a disastrous election defeat, Sen. Alan Cranston of California, the Democrats' Mr. Disarmament, was celebrating his first surprise victory over the field of presidential hopefuls in the Wisconsin convention straw vote.

Parallels are never perfect in politics. But there are two messages from the British election that have special importance for the Democrats.

One is that in a modern welfare state, even double-digit unemployment is not necessarily fatal to a conservative regime. The cushioning of jobless benefits defuses the anger and reduces the visibility of the unemployed. And the reduction of inflation, the other side of recessionary economics, brings big political benefits among the vast majority of voters who are either employed or retired.

The second message is that a party can go so far in campaigning against nuclear weapons, and no farther. When it strays beyond the limit, it goes over the edge of Credibility Cliff.

Which brings us back to Cranston and Foot. Cranston does not favor unilateral nuclear disarmament, as Foot does. But Cranston does say that the reason we have gone more than 10 years without a ratified arms control agreement with the Soviet Union is not Soviet aggression in Afghanistan or the masssive Soviet nuclear and conventional arms buildup threatening Europe. It is simply, Cranston says, that "no president of either party has given that objective (nuclear disarmament) the priority it deserves."

He has promised to rush from the Inaugural stand, if he becomes president, into an unstructured summit conference with Yuri Andropov, to see what they can work out between them, man to man. And he has embraced the concept of a "nuclear freeze," which was part of the Labor Party platform, too, with such fervor that many activist Democrats believe, as Foot's followers did in Britain, that he must be more committed to the cause than anyone else around.

Much has been made of Foot's ineptitude as a campaigner and a party leader. But that overlooks the fact that in his own audiences, where anti-nuclear activists were always out in force, Michael Foot drew nothing but cheers. What he--and they--did not realize was that the country had another view.

The activists who turned out at the Milwaukee convention to give Cranston his victory are much the same people. We have seen them before--literally the same people, in many cases--when George McGovern was rolling to the Democratic nomination in 1972. We have seen them in Wisconsin, whose primary, McGovern wrote, "demonstrated the essential soundness of the strategy that was to win the most unlikely presidential nomination in memory."

That strategy is to find an issue--preferably one of "moral" and not just "political" dimensions--that turns on the activists of the Democratic Left. For McGovern it was the Vietnam War; for Cranston, the nuclear freeze.

There is nothing wrong with it as a strategy for nominating convention politics. Thirteen years ago this summer, when McGovern held the first planning session for his 1972 campaign, his manager, Gary Hart, defined the strategy very simply. "It was to preempt the left wing," Hart said, according to the minutes of the meeting quoted by historian Theodore H. White, and then move against those to his right.

Cranston's avowed strategy for 1984 is the same: first to wrest away from Hart, the senator from Colorado, the banner of the party's left-wing activists, then to undermine Walter F. Mondale (who Cranston's strategists see as an even more fragile front-runner than Edmund S. Muskie was in 1972) and finally to confront Sen. John Glenn of Ohio as the last barrier to nomination.

What Cranston is saying today is almost exactly what McGovern said in 1970 at his Maryland Eastern Shore home, according to the minutes quoted in White's book: "My one unique position," McGovern said, "with reference to the potential competition, is . . . that while I might be the most left-leaning candidate, I am also the most reconciling candidate."

That is the essence of Cranston's pitch. Interestingly, it was also the hope of those who put Michael Foot into the leadership of the Labor Party in Britain two years ago. They argued that because Foot was old and had acquired a moral authority from his role in the battles of the past, he could make the policies of the party's left wing palatable to the rest of the electorate. It did not work.

Now that Cranston has gained a large tactical victory in Wisconsin, he will face increasing pressure to distinguish himself from McGovern and from Foot. The extent to which he can do so may determine how far he can push the advantage he has gained.