NEW YORK — The Washington Post Co. is putting Newsweek up for sale in the hope that another owner can figure out how to stem losses at the 77-year-old weekly magazine.

The publishing industry has been struggling as businesses cut back on ad budgets during the recession. But Newsweek, along with Time magazine and US News & World Report, faces a particular challenge finding a relevant niche in the age of up-to-the-second online news. Once handy digests of the week's events, they have been assailed by competitors on the Web that pump out a constant stream of news and commentary. Despite staff cuts, Newsweek has remained a drag on its parent company, which is also struggling with ad declines at its namesake newspaper.

The Post Co. said yesterday that it has retained the investment bank Allen & Co. to help find a buyer for the magazine.

With advertising revenue falling across the industry, Newsweek has been piling up losses since 2007 and expects those losses to continue this year. It did not reveal specifics, but results from the first quarter are due out tomorrow.

The Post Co.'s magazine division had an operating loss of $29.3 million in 2009, compared with a $16.1 million loss the year before. Newsweek sold about 26 percent fewer ad pages in 2009, according to the Publishers Information Bureau. That percentage decline was consistent with the industry average.