MetLife Inc, the largest U.S. life insurer, said on Monday it expects operating profit to increase for the fourth quarter and full year, helped by unusually strong investment results.

The New York-based company also expects in 2008 to buy back $2.2 billion of stock and post a 13 percent to 13.6 percent operating return on equity, down from 14.6 percent to 14.7 percent this year. It set a goal of 15 percent operating return on equity by the end of 2010.

MetLife expects operating profit per share of $1.40 to $1.45 for the fourth quarter, $6.04 to $6.09 for all of 2007, and $5.90 to $6.20 for 2008. Operating profit per share was $1.36 in the fourth quarter of 2006 and $5.21 in 2006, it said.

Analysts on average expected profit per share of $1.44 for the fourth quarter, $6.10 for 2007 and $6.30 for 2008, according to Reuters Estimates. MetLife expects revenue of $34.8 billion to $35.2 billion for 2007, and $37.7 billion to $38.7 billion for 2008, a regulatory filing shows.

MetLife also said it had $204 million of unrealized losses on an Alt-A and subprime mortgage portfolio as of October 31, the filing shows. This portfolio totaled $8.83 billion as of September 30, and included $6.58 billion of Alt-A residential mortgage-backed debt, $2.18 billion of subprime mortgages and $62 million of collateralized debt obligations related to subprime mortgages.

Many companies have suffered losses on below-prime mortgages as the U.S. housing market deteriorated.

MetLife shares closed Friday at $65.59 on the New York Stock Exchange. Through Friday, they had risen 11 percent this year, compared with a 7 percent drop in the Standard & Poor's insurance index .

(Reporting by Jonathan Stempel; Editing by Dave Zimmerman)