Delta Air Lines Inc , the world's biggest carrier, reported a quarterly loss on Wednesday and said it no longer expected to post a profit for 2009 as the recession continued to affect air travel.

Delta, which became the leading airline when it acquired Northwest in October, said its second-quarter loss was $257 million, or 31 cents a share.

Excluding merger expenses of $58 million, Delta said it lost $199 million, or 24 cents per share. Analysts polled by Reuters estimated a loss of 29 cents, excluding merger costs.

In a memo to staff, Delta said the recession has led revenue to fall more than $3 billion in the first half of the year.

We are not planning for any meaningful recovery in the coming months and no longer expect to be profitable this year, Chief Financial Officer Hank Halter said in the memo, which was including in a Securities and Exchange Commission filing.

The airline industry is straining to cut capacity to adjust to lower demand. Delta has announced plans to cut international capacity 15 percent starting in September.

Delta said it would continue to right size capacity and keep unit costs in check, but it reiterated in its staff memo that it may need to cut more jobs.

While we can make no guarantees in the current environment, our goal continues to be to avoid involuntary furloughs of front-line employees, Halter said in the memo.

In May, Delta offered pilots a voluntary separation package in hopes of reducing expenses. But only 215 of the 9,400 eligible pilots signed up, the union that represents them said last week.

Operating revenue for the second quarter was $7 billion, while operating expenses were $6.9 billion, including $1.8 billion for fuel and related taxes.

Delta ended the quarter with $5.4 billion in unrestricted liquidity.

(Reporting by Karen Jacobs and John Crawley; Editing by Brian Moss and Maureen Bavdek)