New York’s MetLife building, the octagonal skyscraper that Pan American World Airways built in the middle of Park Avenue in 1963, may be sold.

MetLife Inc., the biggest American life insurer, is “gauging interest right now” in its signature building, as well as the company’s former headquarters at 1 Madison Ave., spokesman John Calagna said. The MetLife building alone may fetch $2 billion, said Robert White, president of Real Capital Analytics, which compiles data on real estate sales.

New York-based MetLife, which paid $400 million for the 60-story building in 1981, needs to raise cash for its $11.5 billion purchase of Citigroup Inc.’s Travelers Life & Annuity unit. The company is capitalizing on a Manhattan market where space in top office buildings now commands more than $700 a square foot after rarely touching $500 before 2002, Mr. White said.

“The market is enjoying such unprecedented price levels that even owners who were reluctant to sell their most prized possessions can no longer resist the temptation,” said Woody Heller, head of capital transactions at New York commercial real estate broker Studley Inc.

The 808-foot MetLife building would be the most expensive now available in New York and the first to fetch more than $1 billion since Conseco Inc. sold the General Motors Building to Harry Macklowe for $1.4 billion in 2003.

Cushman & Wakefield Inc. is advising MetLife on the potential sale of its headquarters and CB Richard Ellis Group Inc. is soliciting bids for MetLife’s former headquarters at 1 Madison Ave., in the Gramercy Park section south of Midtown. That building may be worth as much as $500 million, Mr. White said.

“We have made no decision about selling either building, and we may, in fact, not sell either building,” spokesman Calagna said. “It’s a very favorable real estate market right now. That’s why we’re exploring it.”

MetLife’s headquarters loom over Grand Central Station to the south and tower above the 565-foot Helmsley building to the north, blocking the view down Park Avenue. Many New Yorkers consider it an eyesore, and architecture critic Meredith Clausen, in a book about the property last year, described it as a “mute, massive, over-scaled octagonal slab.”

Objections raised when the building’s plans were first made public in 1958 failed to derail the project. Architects Walter Gropius and Pietro Belluschi had enough “star power” as icons of the Modernist school that construction went forward as planned, Ms. Clausen said.

Helicopter service from the building’s roof to John F. Kennedy International Airport was halted for a second time in 1977, after five people died in an accident that sent a rotor blade flying to the street below. MetLife replaced the building’s famous block white “PAN AM” letters with its own in 1993.

“There aren’t but a limited number of properties that you can see a picture of, and you know exactly what that building is,” Mr. White said.

MetLife said last month that it planned to sell as much as $3 billion in assets to fund the Travelers deal, the company’s biggest-ever acquisition. In 2001, MetLife moved 962 workers from the Madison Avenue tower to a warehouse in Long Island City to take advantage of $30.8 million of tax incentives and grants, and it now occupies only a few floors of the Madison Avenue building. One Madison, which was the world’s tallest building from its 1909 completion until the Woolworth Building surpassed it in 1913, may be even more appealing to investors, Mr. White said, since it was leased in its entirety to Credit Suisse First Boston in 2001, a low credit risk tenant.

At $2 billion, the MetLife building would sell for about $715 a square foot. In 2002, Citigroup sold its Park Avenue headquarters for $630 a square foot. A year later, The GM Building fetched $780 a square foot, and in 2004 Equity Office Properties bought the Merrill Lynch Financial Center on New York’s Fifth Avenue for $784 a square foot.