NEW YORK — Tribune — owner of the Los Angeles Times, Chicago Tribune, Baltimore Sun and other dailies — filed for Chapter 11 bankruptcy Monday, the first major newspaper publisher to take such a step since the Internet plunged the industry into a desperate struggle for survival.

The media conglomerate was smothered by a drop-off in advertising and a crushing $13 billion in debt from the company's takeover a year ago by Chicago real estate mogul Sam Zell.

Chapter 11 would buy the Tribune time to put its finances in order. Analysts said the company will almost certainly have to sell off some of its major holdings — and that could prove extremely difficult because of the bad economy and the poor outlook for newspapers.

Tribune employees, who received an ownership stake in the company when Zell came in, could also see the value of their holdings wiped out.

Tribune, which has 20,000 employees, owns baseball's Chicago Cubs as well as 10 daily newspapers, including The Hartford (Conn.) Courant and the Orlando (Fla.) Sentinel, cable channels and 23 TV stations. Its papers' total circulation of more than 2 million puts Tribune among the top three most-read newspaper groups nationwide.

Other newspaper companies also have struggled with heavy debt, a downturn in advertising and the loss of readers to the Internet, but the Tribune was something of a special case.

"Tribune's debt was so outsized and so disproportional to its cash flow compared to these other companies that it can be the sore thumb sticking out rather than an example of the industry," said Ken Doctor, media analyst with Outsell.

Most of the company's debt comes from the complex deal engineered by Zell. The company's lending agreements require it to keep its debt at a certain point relative to its cash flow. Those deals became harder to meet as revenue declined because of the poor economy and competition from the Internet.

Although the Tribune's next major debt payment is not due until June, the company was in danger of missing the financial targets set by its lenders. The bankruptcy filing could give the Chicago-based company some time to press its lenders to ease their targets.