The Obama administration announced details Wednesday of its planned arms package for Taiwan even as China lodged formal protests and Taiwanese officials said they may begin pushing for another deal that would include state-of-the-art fighter jets.

The $5.85 billion arms package proposed by the Obama administration would retrofit Taiwan’s aging fleet of 145 F-16 A/Bs and provide pilot training and spare parts to maintain the nation’s even older F-5 jets and C-130 transport planes. Administration officials have described the sale as a sign of enduring commitment to Taiwan.

U.S. officials have not agreed to sell the island any new F-16 C/Ds, a more sophisticated version, which Taiwan has asked for. The decision has drawn much criticism, especially from members of Congress, who worry that Taiwan’s air power will diminish even as China’s is increasing rapidly.

Taiwan’s Defense Ministry said the proposed package includes an AESA radar system that would allow its planes to detect stealth aircraft, such as the J-20 that China is developing. But Taiwaneseofficials on Wednesday continued to urge Obama to sell them new jets.

Congressional supporters of the idea have filed a bill that would require a sale of F-16s to Taiwan. Without the sale, an F-16 assembly line in Texas faces possible closure.

On the presidential campaign trail, meanwhile, Republican presidential candidate Mitt Romney called Obama’s decision not to sell the requested F-16s an example of “weak leadership in foreign policy.”

“President Obama has ignored Taiwan’s request and caved in to the unreasonable demands of China at the cost of well-paying American jobs,” Romney said in a statement.

A senior U.S. official, who spoke on the condition of anonymity, insisted that Obama has not ruled out such a sale, but military analysts and members of Congress now think that a sale of new F-16s is highly unlikely.

“The State Department has indicated to us that this A/B upgrade was the decision, and that we shouldn’t expect any other decision on the C/Ds. It’s basically a non-decision decision,” said a congressional aide, who spoke on the condition of anonymity to discuss sensitive conversations.

China’s government lodged formal protests with U.S. officials on Wednesday in Beijing and Washington, calling the arms sale a “grave interference” in China’s internal affairs.

If Taiwan does not receive permission to buy the newer F-16s and the assembly line for the jets is forced to close, the island may instead begin requesting a significantly more advanced line of fighters, the F-35, said Andrew N.D. Yang, Taiwan’s vice minister of national defense, speaking at a U.S.-Taiwan defense industry conference in Richmond. The F-35s have more stealth capabilities but have not been deployed by the U.S. Air Force.

An administration official called the idea of selling F-35s to Taiwan fanciful and premature. “It’s like not getting a Prius and asking for a custom-built Ferrari instead,” said the official, who spoke on the condition of anonymity.