London — Britain is on the road back economically. The economy has turned up from the worst recession this kingdom has experienced since the 1930s. But there's more to the new mood of hope than a cyclical recovery. Many now see a good chance for a reversal in this nation's relative economic decline of at least two decades.
''That has been reversed,'' declares Timothy H. Bevan, chairman of Barclays Bank, one of the country's largest banks. ''An enormous amount of national self-confidence has come back.''
He maintains, in effect, that ''Thatcherism'' is beginning to revitalize Great Britain. Margaret Thatcher was swept to power in a landslide electoral victory four years ago. Her Conservative government had a medium-term goal of lowering the inflation rate by reducing money supply growth, public spending, and government borrowing with restrictive monetary and fiscal policies. Her ultimate goals were to give individuals more incentive for work and greater productivity, and to provide greater ''freedom of choice'' by reducing the role and size of government and boosting that of private enterprise.
What causes economists and political scientists to shake their heads in astonishment is the stubbornness with which Mrs. Thatcher has pursued her policies. ''Her consistency through a changing economic environment has been quite remarkable,'' a top government economist noted. In 1981, for instance, the Tory government maintained a deflationary budget and monetary policy in the midst of a downturn.
What is also surprising is that public opinion polls show that Mrs. Thatcher and her government will be returned to office with a large majority in elections Thursday - despite 13.6 percent unemployment, thousands of business bankruptcies , and a drop in industrial production worse than during the Great Depression.
The Thatcher government did not plan such a severe recession. The slump in the world economy and an enormous jump in the value of the pound hit Britain's export industries and companies facing import competition with devastating effect.
That is now history. Is Mrs. Thatcher's drastic economic cure working? Asked this question, several of Britain's top economists gave widely differing grades to Mrs. Thatcher's program, depending to a large degree on their political sympathies or their affiliation with the monetarist or Keynesian schools of economics.
Despite the differences, a few saw the possibility of Britain growing faster for some years than such nations as West Germany and France. ''Britain is in a much stronger position today,'' a high government economist held. Productivity has climbed sharply. Wage costs have dropped. Corporate taxes have been cut. Foreign-exchange controls are gone. So are price controls. Inflation has dropped dramatically. Labor unions have been much weakened by the slump.
''The question remains,'' he cautioned, ''of how much advantage business people will take of the freedom they have got. It is something which we will have to see.''
Already, he claimed, new businesses are being formed at a high rate - as well as failing at record rates. ''We have our first millionaires in manufacturing,'' he said with evident satisfaction.
Roy Batchelor, an economics professor at the City University Business School, commented: ''One thing Thatcher has achieved is to change the attitude to work. People used to believe the world owed them a living. Now they believe in the merit of work.
''Further, he continued, ''The idea that there is a government out there which will give you something at no cost to you - that is an idea which is fading away.
''Prof. Allen Budd of the London Business School confirmed that people no longer believe in economic miracles, that wealth can be created without work.
The economic cost of changing people's minds about their work habits has been enormous. But one government official maintained it had been necessary. Inflation, he noted, had been rising to higher levels after each expansionary turn in the business cycle. Business executives and labor union leaders believed the government would give in whenever wage increases far above the rise in productivity resulted in higher unemployment, by once again pumping up the nation's money supply to reflate the economy.
''Changing those perceptions did involve a certain amount of inflexibility,'' he admitted. ''When you are trying to change perceptions and change the role of government in the private sector, you have to be more stubborn than if you had a longer track record.
''Willem Buiter, an economist at the London School of Economics, has another view. A supporter of the alliance of the Social Democratic and Liberal Parties, he charges the government with having permitted a ''form of industrial vandalism'' when it allowed the pound to float so high on the foreign-exchange markets that much of British industry was made noncompetitive. The Thatcher government did not want to interfere with the workings of the free market. ''When you build a house you don't get a demolition crew in and tear it down,'' Professor Buiter said.
He admits that many of Britain's basic industries were inefficient and overmanned, and that there is some opportunity for growth in newer industries such as electronics.
''There is a shift towards high technology,'' he said. ''But the rate is not sufficient to make up for the massive losses in the economy. I would rather see a chap producing something inefficiently rather than nothing at all.
''Today the United Kingdom has the world's sixth-largest gross domestic product (GDP), after those of the United States, Japan, West Germany, the Soviet Union, and France. It ranks far lower - 19th - in terms of GDP per capita, immediately behind Libya, Finland, and East Germany and immediately ahead of New Zealand, Czechoslovakia, and Italy. The nation's economy grew at a 2.9 percent rate in 1960-70 and just under 1 percent a year from 1971 to 1981. This growth was less than that of most other industrial countries.
Though Britain is coming out of an exceptionally deep recession, most of its economists see only a slow recovery. But there are hints that just as US economists have been surprised by the vigor of the recovery in America, British economists may find their forecasts are too pessimistic.
The government's own rather gloomy forecast of a 2 percent rise in GDP this year over 1982 is close to the average. ''I wouldn't be surprised if recovery is faster,'' one top economist admitted. ''A lot depends on the rest of the world. But there is no prize at this stage for optimistic forecasts.
''Whether the British economy will astound the world and grow at a more handsome rate throughout the 1980s depends much on management and labor working out a more harmonious relationship in the years ahead.