Britain hopes to attract investors by polishing its tarnished world image

The British government wants a new and positive image abroad. It is anxious to attract money for investment. And if possible, it would like to win back some of the intelligence and talent lost in the ''brain drain'' of recent years.

The prime minister, Margaret Thatcher, also wants Britons to have a better image of themselves, and financiers to invest more heavily at home rather than pouring capital into New York and other markets.

According to one Labour Party estimate here, (STR)10 billion (over $17 billion) a year has been flowing out of Britain every year - while 3 million people here are out of work and industry needs more funds.

Mrs. Thatcher thinks victory in the South Atlantic might help change Britain's image, alter the way others think of Britain - and bring capital flowing back here. Yet the determination of the left wing to take over the entire Labour Party opposition, combined with strikes and threats of strikes, continues to win headlines abroad that raise questions about the wisdom of long-term investment in Britain.

The committee that suggests policy for the Labour Party has just outvoted party leader Michael Foot, by a vote of seven to five, to recommend that all major banks be nationalized if Labour should win power again.

A final decision on party policy must be taken by the annual conference later in the year, but the committee vote was a victory for Tony Benn - and another symptom of the difficulty of changing Britain's image.

Mr. Benn cast the issue in terms of how to force British banks to invest in British industry which, he said, had been ''starved of funds'' for many years.

Mr. Foot, forced to vote on one of four options, chose nationalizing one or more major clearing banks should public control (government pressure on the Bank of England as well as other measures) not be enough.

Mr. Benn, the former Viscount Stansgate and Labour Party secretary of state for industry 1974-75, argued that public control would never be enough.

In fact, Labour does not seem likely to win the next election, expected in October 1983. A Labour Party effort in the House of Commons to reimpose exchange controls failed dismally July 12 (the government's majority was 102).

Labour's argument that money was flooding out of The City, (London's financial district) because of a lack of controls, was flatly rejected by the government. The ruling Conservative Party replied that controls had not helped the last Labour government, and were not helping the current French government either.

The government view is that capital will come back when confidence in Britain's long-term prospects increases.

But Mr. Benn continues to loom on the far left. ''Investors look five to 10 to 20 years ahead,'' as one industrial source told the Monitor.

''Mr. Benn may not be influential in this coming election, but who can tell what will happen in the election after that - say, in 1988?''