Fallingwater, Frank Lloyd Wright's architectural masterpiece cantilevered over a waterfall on Bear Run in Fayette County, could soon become a World Heritage Site.

The iconic residence, designed by Mr. Wright in 1935 for Pittsburgh department store owner Edgar J. Kaufmann Sr., is one of 10 Wright-designed buildings on a new U.S. Department of the Interior list of sites eligible for nomination to the United Nations' World Heritage List over the next 10 years.

"This is a very big deal. It brings worldwide attention to the importance of these buildings," said Lynda Waggoner, vice president and director of Fallingwater for the Western Pennsylvania Conservancy. "Locally, we sometimes forget the global profile of Fallingwater."

The World Heritage Site list recognizes the world's most significant cultural and natural treasures, and already contains 20 U.S. sites including Yellowstone, Mesa Verde, Everglades, Olympic, Yosemite and Grand Canyon national parks, the Statue of Liberty and Independence Hall in Philadelphia.

The only World Heritage site designated for its architecture in the United States is Monticello and the University of Virginia in Charlottesville, both designed by Thomas Jefferson.

The United States World Heritage Tentative List that includes Fallingwater was announced yesterday in Washington, D.C., by Secretary of the Interior Dirk Kempthorne.

"I am pleased to be able to take the necessary first step so that these truly significant American natural and cultural properties can be considered for the most prestigious international recognition accorded to properties of global importance," Mr. Kempthorne said. "Each of these sites is important to Americans as well as others around the world."

A country cannot nominate a property as a World Heritage Site unless it has been on its Tentative List for at least a year, and can nominate only two sites in a year.

Ms. Waggoner said there are indications that Fallingwater and the other Wright buildings proposed for the list by the Frank Lloyd Wright Building Conservancy of Chicago will be nominated soon, possibly as early as 2009.

"UNESCO in Paris asked for this nomination of Wright's works," she said. "Modernism is an area where the list is lacking and they asked because they consider Wright America's foremost architect."

Located 50 miles southeast of Pittsburgh near the rural Laurel Highlands town of Mill Run, Fallingwater was built at a cost of $155,000 and was the Kaufmann family's weekend home from 1937 until 1963, when Edgar Kaufmann Jr. donated the property to the Western Pennsylvania Conservancy.

In 1964 the Conservancy opened the house to the public as a museum. It has attracted 4 million visitors over the years, including more than 145,000 last year, its largest attendance total ever.

In addition to the 10 Wright buildings, other cultural sites included on the Tentative List are civil rights movement sites in Birmingham and Montgomery, Ala.; Dayton, Ohio, aviation sites where the Wright brothers pioneered human flight; the Hopewell Ceremonial Earthworks, nine Native American archeological sites between Cincinnati and Dayton; extension of the Thomas Jefferson Buildings site to include the Poplar Forest and Virginia State Capitol in Richmond; and Serpent Mound, a Native American archeological site in Adams County, Ohio.

Natural sites on the new list are the Papahanaumokuakea Marine National Monument in Hawaii; Fagatele Bay National Marine Sanctuary, American Samoa; Okefenokee National Wildlife Refuge, Georgia; Petrified Forest National Park, Arizona; and White Sands National Monument, New Mexico.

World Heritage Sites are designated under authority of the World Heritage Convention, an international treaty for the preservation of natural and cultural heritage sites of global significance that was proposed by President Nixon in 1972. There are 851 listed sites worldwide in 140 of the 184 countries that signed the treaty.