The British press and television have just presented audiences here with another episode in that long running cliff-hanger, "The Perils of Jim Callaghan."

Once again, the Drama followed a well-worn plot line: Liberals to desert pact with Labor; Callaghan government may fall; Liberals decide to stick; Callaghan save.

It is a nice, tidy yarn with a scenario as predictable if less entertaining than the Sam Spewack's classic formula: "Boy meets girl ; boy loses girl; boy gets girl." The comedy here also bears about as much relation to reality as his Broadway shows.

The underlying political fact is that Prime Minister Callaghan appears to have enough votes in Parliament - even without the Liberals - to hang on to office until he decides to call an election.

He is now hinting that will not do so until the spring of 1979. By then, he hopes the expansionary budget he will present this spring will cut Britain's jobless rate and increase real incomes. At 10 Downing Street, his closest aides are convinced that the only way they can be driven from office any earlier is through a desertion of Labor's left wing.

The political arithmetic behind this thinking is as follows: Labor has 308 members of Parliament and counts on two additional Ulster Catholics. That means Callaghan needs only eight more for an absolute majority on any issue of confidence and there are plenty of places to get them.

At the moment, Labor wins 11 from the Liberals on a showdown vote thanks to the agreement this March under which Labor promised to consult with the Liberals in exchange for support. The latest episode was triggered by the anger of a few Liberals over Callaghan's failure to deliver on an esoteric issue, the selection of delegates through proportional representation to the European Assembly. It was beaten by an unusual combination of Conservatives Labor leftwingers.

But since the European Assembly is a powerless Common Market organ and since a majority of Labor deputies actually did support proportional representation, the vote was hardly grounds to break up the Liberal-Labor pact.

More to the point, the Liberals could expect to be crushed if they forced a national election now. The polls suggest they might lose 10 of their 11 seats.

If, despite their weakness, the Liberals should decide to force a vote, Callaghan has a strong fallback position. He has been carefully nurturing and understanding with the 10 Ulster Protestant members of Parliament.

Until recently, these members were staunchly Conservative - wealth businessmen and land owners. Today they are mostly workers, small businessmen and farmers or lower middleclass preachers. Their class origins bring them close to Labor. Moreover, they regard the Tories as enemies because it was Prime Minister Edward Heath who brought down their Stormont Government, the instrument of Protestant ascendancy in Ulster.

More immediately, Callaghan does nothing to offend them. His Ulster minister, Roy Mason, never speaks of reviving a plan to give Catholics as well as Protestants a say in the affairs of the divided province, Mason, moreover, pursues Irish Republican Army suspects with such vigor that Britain could well be brought again before the European Human Rights Commission on torture charges.

So Callaghan can normally count on seven or so of the Ulster Protestants.

In addition, there are three Welsh and 11 Scottish nationalists. They want to see bills enacted giving their ancient kingdoms a measure of home rule and they regard the Tories as foes of this idea. The Scottish Nationalists are a less certain source of Callaghan support however.

Anyway, the Nationalists' potential defection is partly offset by two other Scottish members, breakaways from the Labor Party who usually vote with the government.

The point is that the Callaghan seems confident he can always pick up the few votes he needs to stay in power.

He could, of course, be wrong. The Liberals might conclude that they are losing what is left of their fading political identity because of their close association with Labor. The Ulster Protestants could be forced away by an unavenged IRA outrage. The Scottish nationalists might decide that the sooner an election the better.

But at 10 Downing Street, the conviction appears strong that the only real threat lies in 20 or so determined socialists within Labor's ranks, fed up with Callaghan's cautious government and eager to replace him with a more leftist leader. A score of these, sitting on their hands in a confidence vote, could bring Callaghan down before he wants to go.

At the moment, however, the crisis talk has little substance. It still looks as if Callaghan can, if he wants, put off an election until the fall of 1978 or even 1979.