The cooks, cashiers and others who work in 45 federal cafeterias in the Washington area voted overwhelmingly last night to walk off their jobs Thursday.

Their employer, a private contractor called Government Services Inc., has one last chance today to make them a better offer on wages, medical benefits and other provisions before their contract runs out at midnight tonight, officials of Local 25, the Hotel and Restaurant Workers Union, said after the vote.

The cafeteria workers have not struck since 1948. Many of the more than 1,200 workers make between $3.50 and $4 an hour, officials said.

The company's last offer was for an increase of 15 cents an hour, which is "totally unacceptable," chief negotiator Minor Christian said.

"These are people whose entire wages go for the necessities of life. We're not even considering the president's guidelines (a 7 percent limit on increases). The president was not talking about poor people," Christian said.

Some of the more than 600 workers who packed a ballroom of the Mayflower Hotel for the vote expressed fear of a strike as they went in. "I want more money, but I don't want a strike. Can't afford that with my family," one woman said plaintively.

No spokesman for Government Services Inc. could be reached for comment.

Union officials told the workers to report for work Thursday and wait for the word.