DETROIT, July 23 — The handshakes and polite jokes are over. Now the real work begins for Detroit’s beleaguered automakers and the United Automobile Workers union.

Union leaders will meet with negotiators from the three carmakers in the coming days to begin exchanging contract proposals. The current pact, reached in 2003, expires Sept. 14.

Talks opened Monday at General Motors and the Ford Motor Company, after starting Friday at the Chrysler Group.

After meeting with Ford officials, the president of the U.A.W., Ron Gettelfinger, said Monday that he wanted the new contract to last four years, like the one it is replacing, even though some analysts have suggested that a shorter agreement would be in the carmakers’ interest.

Mr. Gettelfinger also suggested that the companies could reorganize without further sacrifices by the union, which agreed to cuts in medical coverage at G.M. and Ford in 2005.

He noted the $23 billion that Ford raised recently by mortgaging most of its North American assets after posting a $12.6 billion loss last year.

“They’ve got a lot of cash,” Mr. Gettelfinger said. “That’s not an issue for us right now.”

But Joe W. Laymon, Ford’s group vice president for human resources and labor affairs, said the proceeds of the mortgaging were needed to finance the company’s revamping, calling it “the largest home loan in the history of mankind.”

Mr. Laymon acknowledged that the union had helped Ford cut costs.

“The harsh reality, though, is that with all the progress that we’ve made together is that we still have a lot to get done in these negotiations,” he said. “Our shared vision is to do nothing less than to reinvigorate an iconic American company.”

Mr. Gettelfinger, too, sees the outcome of the negotiations, which have been called the most crucial in at least a generation, as having a larger purpose.

“We are fighting for good jobs for America,” he said. “It’s not just about us. These negotiations are about everybody.”

The Detroit carmakers say they must cut costs deeply to better compete with Toyota and Honda of Japan, whose costs at nonunion plants in the United States are lower than at their American counterparts.

Although G.M. says its own revamping is on track, its chief negotiator said the company could not afford another contract as generous as the current agreement.

“While we have made significant progress as a company, there’s still a lot more work to do,” said Diana D. Tremblay, G.M.’s vice president for labor relations for North America. “We need to make some changes to make the business sustainable in the long term.”

Ms. Tremblay said health care was one issue that must be addressed, particularly for retirees, who outnumber active workers for the first time in the union’s history. She said retirees accounted for $3 billion of the $4.8 billion that G.M. paid last year for health care.

About 250 retirees from several G.M. plants in Michigan were present for the opening of negotiations Monday. Lyn Barry, 68, who worked at a former spark-plug plant in Flint, Mich., said he was optimistic about a new contract but was also realistic.

“We hate to keep losing more and more,” Mr. Barry said. “But if you keep all your benefits and the company goes broke, it doesn’t do you any good.”

If talks stall, Mr. Gettelfinger insisted that he would be willing to call a strike, even though many experts have played down that possibility given the carmakers’ fragile state.

“A strike remains a possibility,” Mr. Gettelfinger told reporters. “That’s always an option that we have.”

Later in the day, at Ford’s headquarters in Dearborn, union negotiators shook hands with the company’s executive chairman, William Clay Ford Jr., and chief executive, Alan R. Mulally. While reaching across the conference table, Mr. Ford joked, “If you pull hard, I’ll be on that side.”

Mr. Mulally, after photographers asked him to pose with Mr. Gettelfinger a second time, quipped, “I look better than Rick, huh?” — a reference to the participation of G.M.’s chief executive, Rick Wagoner, in the G.M. ceremony hours earlier.

Although the G.M. handshake took place in front of the entire media corps, only photographers and television camera operators were allowed to witness the Ford ceremony because the room was too small to hold them as well as print and broadcast reporters, Ford officials said.