The Miracle Maestro" proclaimed glossy brochures, hailing the arrival in March of a new car intended to reverse the fortunes of BL, the state-owned British auto maker that has soaked up about $3 billion in public money since 1975 and has yet to turn a profit.

Hopes were high here, one of the centers of Britain's troubled auto industry. The Maestro got good reviews for style and handling. After reducing the Cowley work force by 30 percent in recent years, a thousand jobs were added. About $30 million was invested in retooling and design for the medium-priced line.

Harold Musgrove, chairman of BL's Austin-Rover division, boasted that labor relations were better than ever. In 1982, he said, the company--formerly British Leyland--was "99.5 percent dispute-free."

Only a month later, the optimism was crushed. The 5,000 workers at Cowley's assembly plant walked out because management had demanded they give up a traditional three minutes twice a day of "washing-up" time. The company wanted work from "bell-to-bell," saying it could get 100 more cars off the line each week. The workers said they were being harassed.

The strike lasted four weeks and two days before the workers reluctantly agreed April 27 to go back to work during a month-long cooling-off period.

The conflict seemed destructive on all counts. Why would a reasonable management threaten BL's incipient revival by a move the workers were bound to resent? Why would the workers imperil their jobs in a time of high unemployment? Haven't labor and management learned anything from the years of Britain's industrial decline?

Prime Minister Margaret Thatcher's Conservative government says the worst of the country's long recesssion is over. The Confederation of British Industry in a report last week showed the first "substantial recovery of confidence" in the economy in seven years.

But the strike at Cowley shows how fragile that turnaround can still be. The patterns of class conflict in Britain remain deeply rooted.

As the economy improves, many specialists expect further damaging tests of strength in the work place. Power shifted to management in lean times. Hundreds of thousands of jobs were lost in Britain, probably forever. Now, as demand starts to pick up for so basic an industry as automobiles, workers may well flex whatever muscle they can muster. The result, warned Sir Terence Beckett of the business federation, will be "industrial suicide."

In this case, instead of churning out Maestros to meet impressive consumer interest, BL lost about $120 million in potential revenue as a result of the walkout, according to the company's chief executive, Ray Horrocks. Dealers reported that buyers were cancelling orders because of shortages. The workers lost four weeks' pay, about $600. The issue of washing-up times remains unresolved during the cooling off period.

But worst of all has been the impact on morale. A company poised for recovery has stumbled once again.

At the gate at lunch time and in dingy Johnson's Cafe, a short walk away, the workers' mood is bitter. No one is willing to be quoted by name.

"There are repercussions for speaking out," said a l5-year employe. "The foremen treat us like dirt. They curse at us. The washing-up time was the last straw. Enough was enough."

But this man said, as did virtually all the others, that in the end, they were certain to lose their protest.

Finally, the workers overruled their own shop stewards who had turned down the last company offer for a joint labor-management team to study the washing-up problem and other grievances.

"I was unemployed 18 months before this job," said a 29-year-old. "I couldn't deal with that again." How much time each day, another man wondered with a cynic's empty laugh, does management spend "washing up?"

As management sees it, the core of the dispute is productivity. Most of the graph figures for BL's performance since the late 1960s have been down: total output of cars and commercial vehicles, share of the British market (once over 40 percent, now less than 20), number of employes. Tough-minded leadership has pared back in a determined effort to salvage at least something.

There are a few bright spots. The Jaguar division is making money and there is a possibility it will be sold into private hands. The company has signed a joint-venture agreement with Japan's Honda to develop a new executive car by 1985.

Yet productivity comparisons to other countries remain stunningly bad. A recent study by a professor at Britain's East Anglia University showed that it takes six times as many workers to produce a British-made car as a Japanese one and three times as many workers as in West Germany.

Reducing that gap is crucial to Britain's recovery.