BEIJING, July 24 (Reuters) - U.S.-based Westinghouse Electric will sign a multi-billion-dollar deal on Tuesday with Chinese partners to build four nuclear reactors in eastern China, industry officials say, finalising a pact agreed between Beijing and Washington seven months ago.

The deal, estimated in the past at some $8 billion, is expected to warm relations between the world's top energy users amid recent disputes over issues from the yuan currency and China's bloated trade surplus.

Westinghouse, owned by Japan's Toshiba Corp., will build four 1.1-gigawatt reactors using its advanced AP1000 design, a technology the Pittsburgh-based company said is the basis for nearly half of the world's operating nuclear plants.

A senior industry official told Reuters that construction would start in end-2009 or early-2010 and the first reactor was slated for operation in 2013.

"It should be the final commercial contract, which means parties have agreed on the technical plans and finalised the investment," said the official familiar with the development, who declined to be named.

A signing ceremony was scheduled for later on Tuesday in Beijing.

The deal will reaffirm China -- now a laggard in the nuclear sector -- at the forefront of a global trend towards increased use of atomic power, touted by many nations as the cleanest and cheapest solution to the world's strained energy industry.

But fears about nuclear safety have resurfaced after an earthquake hit Japan last week, causing leaks of water with low-level radiation from Tokyo Electric Power Co.'s plant in the northwestern city of Kashiwazaki.