(Adds details on tentative agreement, end of strike)

By Joseph White

DETROIT, Dec 8 (Reuters) - Union workers at Nexteer Automotive Group Ltd's plant in Saginaw, Michigan, reached a tentative agreement on a new contract late on Tuesday and will return to work after a nearly day-long strike, officials from the United Auto Workers said.

About 3,200 UAW-represented Nexteer employees at the company's main North American factory walked off the job early on Tuesday after rejecting an earlier contract proposal. The walkout halted production of steering systems and other components essential to vehicle production by General Motors Co and other automakers.

Later in the day, leaders of United Auto Workers' union Local 699 announced on their Facebook page that a new tentative agreement had been reached, and instructed members to report for work starting with the third shift on Tuesday night. The UAW did not disclose details of the new agreement, which is subject to ratification by members of Local 699 and could be rejected.

The strike at Nexteer came after UAW-represented workers at the Saginaw factory on Sunday voted down a previously proposed contract by a wide margin. Local 699 leaders posted a tally sheet of the vote on Facebook showing 3,103 "No" votes to only 80 "Yes" votes.

Nexteer, controlled by a unit of Aviation Industry Corp of China, was formerly part of GM and remains a major supplier of steering systems and related hardware to the automaker. Nexteer supplies steering systems for GM's profitable Chevrolet Silverado and GMC Sierra pickup trucks.

GM and Fiat Chrysler Automobiles NV said in statements earlier on Tuesday that they were monitoring the situation at Nexteer. GM also said its production had not been disrupted.

FCA said Nexteer supplies parts to several of its North American factories.

Ford Motor Co said in a statement that Nexteer's Saginaw facility "does not directly support any Ford operations in North America." (Editing by Diane Craft, Frances Kerry and G Crosse)