BLACKPOOL, England (AP) _ The annual conference of the opposition Labor Party endorsed on Monday key proposals to tone down left-wing policies in a bid to end nearly a decade of Conservative Party government.

Leftists, already soundly defeated in a bid to oust Labor leader Neil Kinnock, accused him of ditching cherished socialist principles after three successive election defeats by Prime Minister Margaret Thatcher.

The review, the first stage of a two-year process, includes dropping a commitment to renationalize all state-owned industries sold by Mrs. Thatcher and also accepts some of her drastic curbs on the powers of labor unions.

''We don't have to cling to the past, terrified to move,'' Labor's election campaign manager, Bryan Gould, told more than 1,000 delegates at the Winter Gardens conference center in this north England resort.

''There is a bright socialist future for this party and this country if only we have the courage to think for it,'' Gould said.

A succession of left-wing speakers denounced the policy review document, ''Social Justice and Economic Efficiency,'' which stresses the role of capitalism while promising greater state control of the economy.

To cheers from supporters, miners' leader Arthur Scargill, a pro-Marxist, said the new policies were ''a clear departure from the basic principles and traditions of our party.''

''I didn't join this party to have a yuppieland approach, to run capitalism better than the Tories,'' said Scargill. ''I joined this party to change this society and create a socialist alternative.''

Delegate Matt Wrack described the document as a ''pompous, self-important, mendacious load of drivel.''

Kinnock ordered the review after Labor's last election defeat in 1987.

The new proposals, released last spring, also stipulate tax rate ceilings of 50 percent to 60 percent, compared with 86 percent under the last Labor administration, which lost power in 1979.

The proposals are the first stage of a two-year process. The rest of the review, including the party's controversial pledge to scrap nuclear weapons unilaterally, is due to be published next spring, with final decisions made on the whole package at Labor's 1989 convention.

The next election must be held by 1992, but it is likely in 1991.

Labor's constitution still has a basic Marxist-style tenet adopted in 1918, which calls for ''common ownership of the means of production, distribution and exchange.'' Kinnock and his top aides insist that a mixed economy of private and state control does not conflict with the tenet, known as Clause 4.

Under the new policies, a Labor government would only nationalize giant utilities, such as British Gas, sold by Mrs. Thatcher. She plans also to sell the national electricity utility.

But the rest, which include British Airways, a national freight service, Jaguar cars and the state's remaining share in British Petroleum, would be left in private hands. One in seven voters has bought shares in the big Tory government sales alone.

Kinnock plans to use his resounding defeat of a leadership challenge by leftist Tony Benn as a mandate to press on with what he calls a party platform based on ''realism.''

In a ballot Sunday night, Kinnock won 88 percent support from an electoal college consisting of labor union leaders, the party's 228 members in the 650- seat House of Commons, and local party branches.

The Labor Party was founded by the trade unions at the turn of the century and they continue to fund it. Benn pledged to fight on and maintained Kinnock's tactics would not win the next election.