The Labor government conceded today that its pay curb agreement with the unions - the centerpiece of economic strategy here for two years - had expired. Even so, Denis Healey, chancellor of the Exchequer, pleaded for anti-inflation wage bargains of less than 10 per cent.

To sweeten his appeal, Healey announced a $2.2 billion package of tax cuts, subsidies and spending increases. There is little reason, however, to think his plea will be heeded.

By the end of the day, union leaders ranging from militants in the miners to moderates among government workers were declaring that 10 per cent was not nearly enough. Their members, they said, had a lot of catching up to do.

Britain's economy has been so transformed by the inflow of North Sea oil, however, that it is entirely possible that the wild inflation here could be reduced even with pay increases well above Healey's 10 per cent target.

A year ago, if Healey had announced he could not extend the deal with the unions and that he was boosting demand anyway, panic would have struck. The pound would have fallen precipitously in foreign exchange markets and the world currency system would have trembled.

Today, the banks, multinational corporations. Arabs and other big foreign exchange holders, greeted the news from here with a "ho hum." There was little dealing, the pound was steady and ended the day near the $1.72 it has been at for months. This was the market's way of saying that the pay curb was no longer central to Britain's fate.

Indeed, a year ago, exchange markets ignored both the curb and the coming flow of oil. The Arabs, the banks and the corporations did push the panic button and drove the pound as low as $1.56.

It was this fall in the pound that drove up the price of things Britain buys abroad - food and raw materials - and was largely responsible for the inflationary surge that now afflicts the country.

Although prices here are rising at a yearly rate of about 17.5 per cent - nearly twice the pace in other European countries - the pound is strong. British oil meets half the nation's needs now - replacing oil that had to be bought with foreign exchange - and will soon supply all the domestic demand. That means, that the foreign demand for pounds exceeds the supply, and the currency could even rise.

Even so, Healey insisted in the Commons today that wages were the key to prices here. He tried to put the best face on his failure to persuade unions to accept a third year of wage restraint, saying that he looked for "an orderly return to [unfettered] collective bargaining." He called for increased earnings of no more than 10 per cent in the year ahead, a figure that implies wage hikes of only 7 per cent.

As a carrol, he offered this package to stimulate demand and cut unemployment: Slashes in bottom bracket income taxes of $1.6 billion, $500 million in enlarged family allowances: free school lunches for another half million children: a small subsidy for milk buyers, and modest job programs for building and machine-tool workers.

There is so much slack in the British economy - the jobless rate is at 5.7 per cent or more than 7 per cent by U.S. (measurements) - that the extra demand could generate greater production rather than increase prices.

Prime Minister James Callaghan is staking his government's future on Healey's package. The Commons will debate the program Wednesday and then vote on it. Callaghan has said he will regard the outcome as a vote of confidence, meaning he will resign if he loses.

His fate lies with the Liberals, who fear an election as much as Labor, and his own party's especially vulnerable life wingers. Callaghan would able left wingers. Callaghan would be believed he would win it.

The pay deal with the unions - called the "social contract" here - fell apart last week. Then members of the Transport Workers, Britain's biggest union, voted against their retiring chief, Jack Jones, and insisted on a free hand in bargaining. Ironically, Jones had been called "the most powerful man in Britain" until his defeat.

The plight of workers here made it unthinkable that the pact could be extended for a third year. By April, unions had observed the pay limits so scrupulously that their earnings in pounds were only 11 per cent above a year ago. But consumer prices had shot up 17.5 per cent.

In other words, workers were suffering a six per cent fall in real income.

Most international economic organizations have forecast relatively bright prospects for Britain. But these forecasts were based on the hope that a third year of wage restraint would take place.

If the unions now push for gains of more than 20 cer pent again, the prospects are grim. The government will be faced with the Hobson's choice of printing the money to satisfy these demands and lifting inflation to dizzying heights. Or the government could relentlessly squeeze the economy and enlarge jobless rolls that are already too large.

But if the unions settle for something less - even if it is more than Healey's 10 per cent target - the outlook here is better than it has been. Oil and the exchange market's recognition of its existence gives the government some maneuver room.