The Times, Britain's oldest and best known newspaper, has been saved from its latest threat of closure by nearly completed negotiations to cut costs by reducing its labor force, owner Rupert Murdoch said today.

"I'm happy to say the Times has been saved," Murdoch, the Australian press baron, told reporters at London's Heathrow Airport before flying to the United States, where he owns the New York Post and other newspapers.

Murdoch said negotiations he expects to be completed this weekend with unions representing 2,600 employes of the Times, Sunday Times and several supplements would achieve at least several hundred of the 600 job losses he sought a month ago.

"There will be 360 immediate layoffs and the rest will follow, and we shall be losing part-time workers as well," Murdoch said.

Murdoch had threatened twice before during disputes with the unions to close The Times. He said today that whether the paper "is saved for all time depends, of course, on economic factors, as it does in any business."

The agreed staff cuts would achieve about 70 percent of what Murdoch originally sought, reducing his wage bill by about $14 million between now and the end of the year. The Times is reported to have lost between $20 million and $30 million last year, however, and stockbrokers specializing in the newspaper industry question whether the trimming will be sufficient to make the 197-year-old paper profitable. "There is still a lot of overmanning there," one analyst said.

The Times, a relatively low-circulation national newspaper appealing to affluent, establishment readers, has eaten up profits from Murdoch's successful down-market papers here, including Britain's best selling daily, the tabloid Sun, which has a circulation of more than 4.1 million copies.

Since Murdoch bought The Times and moved noted journalist Harold Evans from the profitable Sunday Times to be its editor, circulation increased from an average 279,000 daily in the second half of 1980 to 298,000 during the same period last year. But this is still below Evans' target of 350,000, and advertising has not increased significantly yet.

Murdoch refused to answer questions today about persistent rumors that Evans may be forced out despite recently being named Britain's "editor of the year." The Times has become noticeably livelier and newsier under Evans, but competing editors contend that it also has become less reliable as Britain's traditional newspaper of record.