DETROIT — The United Auto Workers union won $5,000 signing bonuses for its workers and a promise to reopen an assembly plant in Tennessee as part of its tentative new contract with General Motors, according to people briefed on the negotiations.

In what is being viewed as a landmark deal, the union also preserved health care and pensions and improved profit-sharing for its roughly 48,000 members who work at G.M.

Officials at G.M. and the union declined to discuss specific terms of the deal. But people briefed on the negotiations said that workers would receive a signing bonus of $5,000 in lieu of cost-of-living wage increases. Entry-level workers, who are paid about $14 an hour, are expected to receive an increase of $2 to $3 an hour.

The company has also agreed to reopen its idled assembly plant in Spring Hill, Tenn., the people said.