The number of unemployed workers jumped to its highest total in British history last month, reaching 13.8 percent of the work force, or nearly one worker out of seven.

According to government figures released today, the September figure grew more than 100,000 over August to more than 3.3 million people out of work and claiming unemployment benefits.

The figures came as a blow to Prime Minister Margaret Thatcher's government as her Conservative Party prepares for its annual conference next week. They are likely to fuel those in the party who believe Thatcher's tight budget policies must change if the Conservatives are to win reelection.

Repeated polls show unemployment has become the government's biggest political problem. More than any other issue, it has moved opposition parties to start campaigning in earnest at least two years before the next general election.

The opposition Labor Party lost no time condemning Thatcher at its own party conference in Bournemouth. Labor's employment spokesman, John Prescott, quickly noted that the figure had set a national record "higher than we had in the 1930s."

Some increase was anticipated, as the September figures include youths who left school this spring but were not allowed to apply for unemployment benefits until fall. Government officials quickly pointed this out, and noted the seasonally adjusted figure for adult unemployment actually showed a decrease of nearly 3,000.

"Of course the headline figure was high," said Employment Secretary Lord Young. "But you know the most important figure in all of this is vacancies, and the vacancies are the highest figure since February 1980."

Although its jobless rate is the highest in Western Europe, Britain has created more new jobs over the past several years than any other Western European country. Many of those jobs are specialized and skilled positions in high-tech industries in the south.

The legions of unemployed consist primarily of unskilled youths, and workers laid off by large industries in the north and central regions.

The Labor Party, and many economists here, believe that the only way to promote widespread recovery in employment is to pump more money into the economy through public employment and public investment in industry.

Labor's economy spokesman, Roy Hattersley, today proposed a national minimum wage, a "National Investment Bank" to finance job creation and a get-tough policy with businesses that invest their money abroad, including a reimposition of currency controls dropped by Thatcher. Labor promises it would create at least 1 million jobs during its first year in office.

The Thatcher government, like its counterpart in Washington, has committed itself to reducing public spending only to see unemployment soar. Much of the budget is spent on unemployment and other social benefits that the government also wants to cut.

The government believes the economic and employment pump can only be primed over the long term, through tax cuts and job creation in new, smaller industrial sectors.

None of Britain's big companies are adding jobs, Young said. "All of them are shedding labor and must shed labor because of new technology. The vast growth of employment . . . comes from small firms, from self-semployment, and that's the way, the solid way in which we build up employment."