A US-Australia free trade deal, criticized by some Australians who say it favors US exporters, will be signed here May 18, officials said Monday.

US Trade Representative Robert Zoellick and Australian Trade Minister Mark Vaile will sign the deal, which would still require ratification by US and Australian lawmakers.

"American businesses, workers, farmers and consumers will soon have significantly increased ties to this good friend and valuable trading partner," Zoellick said in a statement.

"Once Congress approves this agreement and it goes into effect, there will be an immediate cut in Australian tariffs on our manufactured goods, providing our manufacturing industry with a helpful boost."

Under US law governing trade agreements, the deal could not be signed before May 14.

Zoellick said the two sides were signing the agreement May 18 because it was the "earliest possible date."

The agreement, reached in February after 11 months of negotiations, is under scrutiny in Australia.

Opposition politicians and some Australian economists doubt its claimed benefits, arguing that it excludes some sectors, will hurt

others and may damage Australia's trade relationships in Asia.

The Australian government has already been forced to compensate canegrowers with a four-year, 440 million Australian dollar (320 million US) rescue package after sugar was excluded from the deal.

But an Australian government-commissioned study found last week that the proposed free trade agreement would be worth much more to Australia's economy than previously estimated.

The Centre for International Economics study said the deal, previously estimated to be worth 2.9 billion US dollars a year, would boost real gross domestic product by more than 4.3 billion US dollars a year by 2014.

Australia is the 13th largest market for American exporters, the US Trade Representative (USTR) office said.

Two-way trade in goods and services amounted to about 28 billion US dollars a year, with the United States enjoying a surplus of nine billion dollars, the USTR said.

Australia is an export market for American aircraft, autos and auto parts, machinery, computers and electronic products, chemicals, and wood and paper pro ducts.

The United States already has free trade agreements with Canada and Mexico under the North American Free Trade Agreement, Chile, Israel, Jordan and Singapore.