Britain's strike-ridden Labor Party government and its trades union allies today issued a 20-page document proposing that government, industry and labor agree each year on how to divide the economic pie.

The cautious government-union statement, riddled with escape clauses, was dictated by the growing voter hostility toward Prime Minister James Callaghan and the trades unions.

Although the statement appeared to be essentially an exercise in public relations, it constitutes a recognition that unfettered collective bargaining can be an engine of inflation, and that something better is needed.

Union chiefs and Callaghan's ministers have spent nearly three weeks discussing the production of a pact to rebuild their waning popularity. The 20-page document that has emerged will not end a single one of ths disputes now in progress or head off those still to come.

But it does contain one proposal of importance. This calls on government, industry and labor leaders to make an annual assessment of the nation's economic prospects.

In Sweden and West Germany, a similar device yields a norm or guideline for wage increases that heavily influences bargaining. But here, too many businessmen and labor leaders are frightened by the notion of a norm for the word itself to be used in the government-union statement. It is, however, implied in the call for a national assessment.

A surprisingly relaxed and jovial Callaghan told a press conference tonight, "I've got a lot of scars on me" for attempting to propose a guideline -- 5 percent -- this year. Whether a pay norm should emerge from the tripartite talks, he said, would be "a matter of negotiation and discussion."

Just as important as the union-government statement is the fact that other forces in Britain's political economy are moving in the same direction. The Confederation of British Industry, spokesman for business, has called for a yearly "national forum" to lay out prospective economic predictions. The CBI shuns words like "norm" or "guideline" too. But again economic predictions must include explicit assumptions about pay levels.

For the opposition Tories, Margaret Thatcher, their leader, has publicly expressed her admiration for the West German technique. Thus all consequential figures here are in agreement but can't speak openly about it.

The strikes here have been propelled by rank-and-file workers fed up with three years of pay restraint. To win their support for annual meetings that produce or suggest new guidelines will take time and education. Callaghan himself said that the projected "national assessment" would instruct, would "get people to understand what we're trying to do."

The likely increase in inflation here after the current strike round may also be a potent teaching instrument.

Much of the government-union statement was written by the unions to head off legislation. Thatcher urges to curb their power. She wants to outlaw secondary boycotts, compel secret ballots before a strike begins, prohibit stoppages in vital services and more.

In contrast, the government-union document simply advises member unions to do most of these things on their own. One exception is the secondary boycott, striking an employer who is not directly involved in a dispute. The paper, at the insistence of the truck drivers union, pointedly endorses the technique.

In the house, Thatcher dismissed the whole exercise as a "boneless wonder." She is expected to make legislation to inhibit unions a major plank in her election compaign this year.