Negotiators for Ford Motor Co and the United Auto Workers talked into Friday morning as the two sides closed in on a labor deal that would cap a historic round of bargaining between the union and the embattled U.S. auto industry.

Contract negotiations at Ford's Dearborn, Michigan headquarters continued as of Friday morning, extending the longest-running negotiating session since UAW President Ron Gettelfinger returned to the talks on Tuesday.

The marathon bargaining session began around 10 a.m. on Thursday, said a person briefed on the talks.

In four days of intensive talks, the two sides made progress on key issues centered on health care costs and Ford's planned plant closings, putting a deal within reach as soon as Friday, the person said.

But the talks remained fluid and it was still impossible to say when or whether a tentative contract could be announced, said the person.

Ford, which has some 58,000 UAW-represented workers, is widely seen as having developed the most collaborative relationship with the union of any of the three Detroit-based automakers in recent years.

But the strength of Ford's ties to the union has also been tested by its push for deeper concessions than those granted to either General Motors Corp. or Chrysler LLC.

Ford's contract with the UAW expired September 14. Both sides agreed to a rolling extension as the union focused its efforts on GM then Chrysler.

GM reached a watershed contract with the UAW in late September after a two-day strike. Under the deal, GM agreed to pay almost $32 billion to set up a trust for retiree health care and offered future investment pledges for U.S. factories.

GM and the UAW are negotiating buyouts targeting the 75 percent of its work force that will be eligible for retirement in the coming four years. That amounts to more than 54,000 of GM's 73,000 UAW workers. Those offers are not expected to be finalized until the Ford negotiations are complete.

Ford, which lost a record $12.6 billion last year, has indicated it was looking for about 8,000 to 10,000 factory job cuts. That would be in addition to the 27,000 UAW jobs Ford had cut as of June.

Moreover, Chrysler's surprise move on Thursday to cut up to another 10,000 UAW-represented factory jobs and eliminate four vehicles from its line-up could complicate the union's bargaining with Ford, analysts said.

Chrysler workers last week narrowly ratified a four-year contract giving the automaker the flexibility to bring in new hires at half the wage rates of current workers and to shift some $19 billion in retiree health care costs to a new trust fund.

Chrysler's immediate move to cut another one-fifth of its factory work force will make it more difficult for UAW leadership to get Ford workers to ratify a contract with sweeping concessions, analysts said.

Ford workers are going to feel a sense of betrayal to a point as well, said Jerry Tucker, a former UAW official who campaigned against ratification of the Chrysler and GM contracts.

Ford has said it will close 16 North American factories as part of its restructuring but has so far identified only 10 of those. Ford has 33 UAW-represented U.S. factories.

The six unidentified plants have now been swept up into the contract talks, with Ford holding out the prospect of more limited plant closings in exchange for other concessions.

Both Ford and UAW declined to comment on the negotiations, citing the private nature of the bargaining.

The UAW has not yet issued a notice terminating its contract extension with Ford, in contrast to the harder line it took with Chrysler and GM. The extension could be ended by either party with a 72-hour notice.

Gettelfinger, who began his career at Ford, has said he wants the automaker to match the broad outline of the UAW's deal with GM and Chrysler. That would include funding for a trust to take over Ford's retiree health care costs.

At just over $70 per hour, Ford's hourly wage and benefit costs are the lowest of the Detroit-based automakers but still well above an estimated $48 per hour for the U.S. operations of Toyota Motor Corp.