Just as President Carter is considering introducing pay guidelines in the United States, leaders of both major parties here have virtually agreed that Britain must continue to following a similar course for the indefinite future.

The great debate over how to manage an economy of big unions and big corporations all but came to end here yesterday at the Conservative Party conference in Brighton.

There, Margaret Thatcher, the Conservative leader who is ritually pictured as an apostle of classical free enterprise, tacitly joined Labor's Prime Minister James Callaghan by endorsing some form of pay restraint.

To be sure, she couldn't say this to the party faithful in so many words. The blunt truth was left to her predecessor. Edward Heath, who shocked the conference two days ago by asseerting that Callaghan's pay policy was correct and that most of the country agreed with it.

Thatcher has an ideological right wing to soothe just as Callaghan must be careful not to offend Labor's equally ideological left.

So she spoke of her belief in "realistic, responsible collectie bargaining, free of government interference." And she denounced "totally rigid policies" that "destroy incentives."

But Thatcher ver carefully avoided using the language her party's right wing loves. She never said that she favored "free" or "unfettered" bargaining. She left herself plenty of room to adopt what she will no doubt describe as a "flexible" policy towards incomes or pay.

This indicates how strongly she believes she will soon replace Callaghan at 10 Downing Street. Indeed, she has every reason to believe she will be there after the next election, in six months or so. Like almost every serious Western leader, she has come to conclude that wages are too important a force in an inflationary world to be left to the untrammeled dictates of giants in the market-place.

The conversion of Thatcher is a noteworthy of development. Britain has been one of the last of the northern European democracies where a serious debate over guidelines or incomes policy has been continuing. The issue has been settled in Norway, Denmark, Sweden. Holland and Germany for some time.

To be sure, in all these countries there is a running debate over technique: Should there be, as in Germany, a set of government wise men advising the unions and employers each year on what the economy can afford? Should there be a single "norm" or should it vary according to productivity and profits? Should the policy be imposed by law or must it gain union and corporate assert? Who should be penalized for breaches - unions, corporations, nobody?

At the Labor Party conference here last week, Callaghan, in an unusually candid moment, acknowledged that guidelines won't work in Britain without union consent. At the moment, it appears that consent is being withheld.

The conference dominated by unions, voted down 2-1 Callaghan's announced policy of limiting increases this year to 5 percent. At the British Ford Motor Co., where a strike has been on for three weeks, union negotiators yesterday spurned an offer of 6.5 percent, well over the limit.

The miners are talking about a 40 percent demand. Machine tools makers are planning a 33 percent claim. On the surface, it looks as if the unions have vetoed the politicians.

But surface appearances are often deceptive. Heath, who was driven from office when he tried to fix a statutory limit on wages, was probably right when he said that most of the country is now behind Callaghan on this one.

Several important union chiefs agree. Moreover, at least in private, they acknowledge that the days of unfettered collective bargaining must be over.

It is only three years ago that prices and wages here were spiraling upward at a frightening 30 percent pace, raising questions about the governability of Britain. Nearly all workers in transportation, communications, energy and other industries are working for the government as employer. Even Sir Keith Joseph, the purest free enterprise thinker in Thatcher's entourage, acknowledges that the government can't be indifferent to the pay scales in nationalized industry. They crucially affect government spending tax and monetary policies.

The fact that the leaders of the two big parties here are moving on convergent paths, just as Heath predicted, is not likely to be noticed in popular political commentary. It relishes conflict and drama and will stress conservative cheers for Thatcher's attacks on a government that sets "a fixed percentage for everyone."

In the same way, popular commentary here focused on the Labor Party's "repudiation" of Callaghan's 5 percent and was puzzled by his post-conference refusal to take any heed of this decision.

Jus"t as the United States, sentiment, right and left, dominates party conferences. But sentimetnal choices here as there, Goldwaters and McGoverns, rarely become leaders and almost inevitably are crushed in elections when they do.

Thatcher celebrated her 53rd birthday yesterday by side-stepping carefully toward the center of British politicis. She edged toward covert, if not overt support for pay restraint. The center is where elections are usually won in two-party systems. Prime Minister Callaghan has now lost his monopoly of this vital point.