WASHINGTON -- Nearly half the Senate urged President Obama on Thursday to authorize quickly the sale of F-16 jet fighters to Taiwan, a request that has been hanging for five years.

Despite an easing of tensions across the Taiwan Strait in the past three years, Taiwan says it needs the 66 planes to maintain a credible defense and provide leverage in negotiations with Beijing. U.S. agreement to the sale, worth billions of dollars, would anger China's communist-led government and would set back improved U.S.-China relations.

"Without new fighter aircraft and upgrades to its existing fleet of F-16s, Taiwan will be dangerously exposed to Chinese military threats, aggression and provocation, which pose significant national security implications for the United States," says a letter, signed by 45 of the 100 members of the Senate, both Democrats and Republicans.

Gary Locke, nominated to become U.S. ambassador to China, told lawmakers Thursday that no decision has been made on the sale, and the request for the F-16 C/Ds still is being evaluated by the Defense and State departments.

He said China should reduce its military deployments aimed at Taiwan.

Taiwan and China split amid civil war in 1949. Beijing regards the self-governing island as part of its territory and has threatened to invade Taiwan should it ever declare independence.

The Obama administration faces an awkward choice. It is obligated under U.S. law to provide Taiwan the means of self-defense. Approving the sale, however, could prompt China to cut military ties that the United States has worked hard to forge as a way of smoothing over tensions in the Asia-Pacific where China's military buildup has caused widespread unease.

The two superpowers also are major trading partners, and China's massive holdings of U.S. Treasury securities help Washington manage its vast deficit.

Democratic Sen. Robert Menendez of New Jersey, who initiated the letter, said it was rare for so many senators, both Democrats and Republicans, to send a message jointly to the administration.

Menendez told Locke at a confirmation hearing before the Senate Foreign Relations Committee that Taiwan had been seeking the fighters since 2006, and the production line for making the fighter jets would be closed without the sale.

"You can be devoured if you do not have the ability to defend yourself," Menendez said.

Locke, who is likely to be confirmed ambassador, responded: "The United States stands with Taiwan to ensure that it can defend itself and that its self-defense capabilities are never eroded."

The senators' letter says China is in the process of deploying next generation Chinese and Russian manufactured ships, fighter aircraft and submarines, and has more than 1,400 missiles aimed at Taiwan.

Last week, a top Chinese general visiting Washington denied China has missiles aimed at Taiwan.

Gen. Chen Bingde said sale of F-16 C/Ds would hurt U.S.-China military relations, but he was not specific.