Prime Minister Margaret Thatcher's crusade for "popular capitalism with its naked appeal to financial self-interest is paying dividends as she launches her campaign for a third term of office.

Neil Kinnock, leader of the Labour opposition, aims to mobilize the compassionate moral majority that opposes what he terms the meanness of Mrs. Thatcher's Conservative administration. Labour, seeking to "bind the wounds of the nation, is basing its campaign on poverty and unemployment.But despite the loss of 2.5 million jobs and the large rise in the numbers living below the poverty line since Mrs. Thatcher came to office in 1979, these issues aren't necessarily vote winners.

The moral majority being courted by Mr. Kinnock has prospered under Mrs. Thatcher and has too much to lose in helping out the minority who are jobless and poor.

The government has made Labour's task that much harder, softening Mrs. Thatcher's uncaring image by taking the brake off public spending next year in what is regarded as the biggest U-turn in policy since she came to power. Bigger budgets for social security, housing, education and health stole the opposition's fire. She can resume her courtship of voters' self-interest with tax cuts in the annual spring budget.

The government's abandonment of its insistence on holding down public spending is seen by MPs of all parties as paving the way for an early general election, probably next summer.

''(Chancellor) Lawson has let loose with an election-winning strategy - public spending plans up by 4.75 billion in 1987-88. With tax cuts on top, the economy will be flying next year, commented stockbrokers Phillips & Drew.

This puts Labour on the spot as it tries to steer voters' attention back to its chosen election issues of unemployment and poverty. There are signs that a sizable portion of the electorate has become bored with something that does not touch their lives. The Conservatives have a clear lead in the four most recent opinion polls after trailing Labour for 18 months.

Labour's plans to tackle poverty have been compromised by Mrs. Thatcher's success in promoting tax cuts. To be successful Labour's program against poverty should involve a major re distribution of income involving sacrifices by its moral majority.

But all Labour proposes is to redistribute the 3.5 million that the richest 5 percent of the population have gained from Conservative tax cuts. No one earning less than 27,000 a year - almost three times the average wage - will pay higher taxes. The transfer of income from the middle-income group has been ruled out for electoral reasons.

Ironically, the Social Democrats, a breakaway party of disenchanted Labour right wingers, suggested that middle-income earners should finance an anti- poverty program. Labour denounced these proposals, which were more egalitarian than its own, forcing an embarrassed SDP leadership to beat a hasty retreat. Both are scared of alienating the new man molded by Mrs. Thatcher.

Reducing unemployment remains a major issue but it appears to be fast losing its electoral appeal, simply because the 85 percent of those with jobs are enjoying steadily rising living standards.

The sharp decline in manufacturing industry has been the main contributor to unemployment. In the past seven years manufacturing output has fallen 9 percent but employment is down by almost 26 percent. This shake-out has boosted productivity by more than 18 percent, enabling companies to offer large pay awards. As a result, average post-tax real earnings have risen by more than 18 percent since 1979, more than in any other major industrial nation, including Japan.

At the same time, welfare benefits have risen in real terms, but they have not kept pace with the income of those in work.

Thus Mrs. Thatcher has succeeded in dividing the working class, Labour's natural constituency, into two distinct groups. The majority is steadily growing wealthier, while the minority is falling further behind.

The Conservatives stole a large number of working class votes from Labour in the 1983 elec tion with their promise to sell state-owned housing to tenants at a large discount to their market value. Labour paid the price for misjudging the mood of its supporters, securing just 39 percent of the votes of trade union members.

More than 1 million tenants have bought their homes and have benefitted

from the spectacular rise in prices in the past three years.

While unemployment remains at a post-war high of 3.2 million, there are signs that the rising jobless trend since Mrs. Thatcher came to power in 1979 is beginning to go into reverse. The government has just announced a big fall in unemployment in October, marking the third consecutive monthly decline. Ministers are confident the figures mark a turning point in the labor market and are looking for further reductions in the months leading up to the general election.

Labour's problem is that it is preaching to the converted: Most job losses have occurred in its strongholds in the north of England and Scotland. Unemployment in Conservative-controlled areas in the South is well below the national average.

Mrs. Thatcher's other electoral weapon is the widespread sale of state- owned industries that has turned millions of working class voters into shareholders with a stake in a Conservative victory. The sale of British Gas later this month will swell the number of individual shareholders to 6 million to 8 million, an average of 10,000 to 12,000 voters in every constituency in the country. These first-time shareholders are a potent political force that could tip the balance in the Conservatives' favor in marginal seats.

Labour has pledged to repurchase some of the privatized shares on the basis of "no speculative gain or exchange them for non-voting stock. For stockholders in the newly privatized firms this could result in large losses.

Labour has ditched nationalization in favor of so-called share ownership that so far has been limited to British Telecom. But the Conservatives have seized on the uncertainty surrounding Labour's plans to warn shareholders of the losses they face if they vote for Mr. Kinnock.

The Conservative Central Office has already written to 10,000 British Telecom shareholders alerting them to the dire consequences of Labour's return to power. A much larger mail shot to millions of first-time shareholders is planned for next year.

The battle lines for the general election were drawn last week when the government outlined its legislative program for the current parliamentary session.

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