UPDATE 3-Times Co says won't shut Boston Globe today

* Boston Globe, main union talks on hold

* Paper says will not file federal shutdown notice today

* Newspaper Guild is sole holdout in talks

* Times shares up 4.8 percent (Recasts, updates shares, adds White House comment)

By Robert MacMillan and Scott Malone

NEW YORK/BOSTON, May 4 (Reuters) - The Boston Globe's biggest union won some breathing space after its owner, The New York Times Co (NYT.N), said it will not file notice of its intention to close the newspaper, at least for now.

Six of the seven unions representing employees of the money-losing Globe reached tentative agreements with Times Co, which has threatened to shut the 137-year-old newspaper unless it agrees to $20 million in concessions.

But the future of New England's largest newspaper remained in doubt on Monday. Leaders of its biggest union, the Boston Newspaper Guild, left talks without a deal amid disagreement over lifetime job guarantees enjoyed by about 190 members, according to a Boston Globe report on the paper's website.

The Guild, representing some 600 workers including the newsroom staff, has sought to preserve lifetime job guarantees, saying their elimination would pave the way for layoffs of some of the paper's highest-paid veteran staff.

"We expect to achieve both the workplace flexibility and the financial savings that we sought from these unions," Globe spokesman Robert Powers said in a statement.

"We are not, therefore, making a filing today" under the federal plant closing law, which requires companies to give 60-days notice to the state and employees before closing a business.

The Times Co had set midnight Friday as a deadline to extract $20 million in cuts from its unions to avoid closing the Globe, which it said could lose $85 million this year if no changes were made. That deadline was extended to Sunday.

Management was "disappointed" not to have reached an accord with the Guild, Powers said.

His statement did not rule out filing a notice to close the paper in the future.

"We are evaluating our alternatives under both the Guild contract and applicable law to achieve as quickly as possible the workplace flexibility and remaining cost savings we need to help put The Globe on a sound financial footing," he said.

WHITE HOUSE EXPRESSES CONCERN