LONDON, MAY 24 -- With Prime Minister Margaret Thatcher's Conservatives regaining some lost ground in recent opinion polls, the opposition Labor Party released a new platform today that revealed as much about the party's weaknesses as its strengths as it moves toward Britain's next elections.

The 20,000-word policy document, issued in a glossy cover and entitled "Looking to the Future," is the culmination of Labor leader Neil Kinnock's three-year effort to win back middle-of-the-road voters who abandoned the party for the Conservatives or for smaller centrist parties a decade ago.

It calls for income-tax cuts for the poor and increases for the wealthy but insists that the vast majority of middle-class earners would not be asked to pay more taxes under a Labor government. It says Labor would repeal the hugely unpopular new local levy system known as the poll tax and replace it with a local property tax linked to income. It also calls for Britain's early entry into the European exchange-rate mechanism, which Thatcher so far has resisted.

The document eschews the word "socialism" -- a doctrine Labor has advocated since its inception in 1900 -- calling instead for a new "partnership" between government and industry. The difference between the Conservatives and Labor, it says, is that "they worship the market; we use it," adding Labor's new motto: "Business where appropriate; government where necessary."

Such policy documents are treated seriously in Britain, and the Conservatives immediately brought forth three cabinet ministers, who branded its pronouncements a sham. Their main criticism was that while Labor was promising not to raise most people's taxes, it was also promising new spending on health, education, welfare and environmental services that would make new tax increases inevitable.

"Labor are still a high-tax, high-spending, high-inflation party, just as they've always been, and it's crystal clear when you look at all the pledges in that document," said Norman Lamont, chief secretary to the treasury. "It cannot be afforded by putting up taxes on a few wealthy people. Taxes will have to go up for millions of ordinary taxpayers."

Anticipating the Labor document, Conservative Party chairman Kenneth Baker unveiled a series of new political posters, including one that read: "Labor's tax plans won't hurt everybody -- only those with jobs, homes and savings."

Baker said the posters were part of his "summer heat offensive" designed to reduce Labor's lead over the Conservatives in the polls. That lead has dropped in recent surveys, from a high of 24 percent in late March to 16 percent this week.

Analysts say the drop partly reflects the nagging feeling among voters that despite their disenchantment with Thatcher, now in her 12th year in office, they still do not trust Labor to manage the country's economy.

Kinnock and John Smith, who would be chancellor of the exchequer in a Labor government, have sought to allay those fears by promising that a Labor government would not fuel inflation by spending more than it could take in in taxes. "We see no virtue whatsoever in making undertakings and then clobbering the economy with higher and higher levels of taxation," Kinnock told reporters today.

The Labor document was careful not to place any price tags on its proposed programs. But financial analysts say the figures suggest most families earning $40,000 or more per year could expect a tax increase under Labor.

The other reason for Labor's drop, analysts say, is that Thatcher's political managers have been able to disguise continuing bad economic and electoral news by deftly manipulating the British press.

Party chairman Baker took the sting out of Conservative losses in last month's local council elections by raising expectations of a Conservative debacle beforehand, then claiming victory when the defeat was a little smaller than predicted. The party did the same with new inflation figures two weeks ago, warning ahead of time that the annual rate could exceed 10 percent. When the actual figure was disclosed as 9.4, the newspapers played it as a minor development.