By Bernie Woodall

DETROIT (Reuters) - A proposed four-year labor contract between Ford Motor Co and the United Auto Workers looked set to be rejected after workers at a large Chicago plant voted against the deal by a margin of more than 2-to-1 late Wednesday night.

UAW leaders have warned rank-and-file members that spurning the deal could jeopardize investments that would sustain U.S. factory jobs and argue that the proposed agreement with Ford would be the richest in history.

But many workers are not satisfied, and have taken to social media to argue that the deal does not do enough to make up for pay and benefits that were sacrificed when Ford struggled to restructure during the last recession.

At the Chicago Assembly Plant, 68 percent of more than 3,000 UAW members voting rejected the contract.

Before the Chicago result was known, when three-fourths of the national Ford union vote had been counted, the contract had been rejected by 52 percent of union members, said Jimmy Settles, head of the UAW's Ford Department.

The vote began at union locals last week and will extend through Friday. A majority of votes is need for the contract to be ratified.

Settles and other UAW officials appealed to Ford workers to support the deal or risk losing some of the $9 billion in investments in U.S. factories that Ford has promised in the agreement.

"I seriously think that if we don't ratify it, that (investment) would be in jeopardy," Settles said. "And that's job security. If they invest in plants, they don’t close plants."

UAW leaders have clashed with the rank and file at all of the Detroit Big Three automakers.

A proposed four-year national contract for hourly workers at the U.S. operations of General Motors Co is in doubt because skilled trades workers have voted against it. UAW leaders are working with GM management to resolve the concerns of skilled trades workers, who repair factory equipment.

UAW President Dennis Williams needed two tries to win ratification of a four-year contract for hourly workers in the U.S. operations of Fiat Chrysler Automobiles NV .

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"WE GAVE UP THE FARM"

Ford has enjoyed robust profits this year as sales of trucks and sport utility vehicles made in UAW factories have boomed.

UAW leaders are concerned they no longer have the leverage to demand higher wages, now that vehicles made in UAW factories account for less than one-half of U.S. auto sales.

Scott Houldieson, vice president of Local 551 in Chicago, where workers voted Wednesday, said members who were rejecting the contract believed it did not make up for the sacrifices that helped save Ford.

"We basically gave up the farm," said Houldieson, pointing to a pay hike they gave up in 2006 and a cost-of-living raise not taken in 2009.

Kristin Dziczek, labor analyst at the Center for Automotive Research, said Ford is not likely to spend more money on a richer contract overall if the two sides return to the bargaining table.

(Editing by Jeffrey Benkoe and Edwina Gibbs)