WASHINGTON, Dec 2 (Reuters) - President Donald Trump's threat to veto a defense bill if it does not repeal legal protections for social media companies faced stiff bipartisan opposition on Wednesday, setting the stage for a confrontation with lawmakers scrambling to pass the massive bill by year-end.

Unusually, members of Trump's Republican Party broke from the president to join Democrats in objecting to his threat to veto the annual National Defense Authorization Act, or NDAA, a $740 billion annual bill setting policy for the Pentagon, if it does not include a measure eliminating a federal law - known as Section 230 - protecting tech companies such as Facebook Inc and Twitter Inc.

"First of all, 230 has nothing to do with the military. And I agree with his sentiments. We ought to do away with 230, but you can't do it in this bill. That’s not a part of the bill," Senator Jim Inhofe, the Republican chairman of the Senate Armed Services Committee, told reporters.

Lawmakers announced on Wednesday that congressional negotiators had completed the conference report on the fiscal year 2021 NDAA, a compromise between separate versions of the bill passed earlier this year by the Republican-led Senate and Democratic-majority House of Representatives.

Congressional aides said the final version of the NDAA does not include the Section 230 repeal demanded by Trump.

The legislation also includes a provision that would strip the names of Confederate generals from military facilities, something that passed both the House and Senate with support from both parties earlier this year, but is also opposed by Trump. The president earlier had threatened to veto the NDAA if it did not allow the Confederate names to remain in place.

'PARTISAN PREFERENCES'

"For 59 straight years, the NDAA has passed because Members of Congress and Presidents of both parties have set aside their own policy objectives and partisan preferences and put the needs of our military personnel and America’s security first. The time has come to do that again," Representatives Adam Smith, the House Armed Services Committee's Democratic chairman, and Mac Thornberry, the panel's ranking Republican, said in a joint statement.

Since it is a conference report, and the result of months of negotiations between members of both parties from the House and Senate, it cannot be amended.

Lawmakers take great pride in passing the NDAA every year. It is a rare major bill seen as "must-pass" because it governs everything from pay raises for service members to how many aircraft, missiles and ships should be purchased, to how best to compete with Russia and China.

This year's bill authorizes the Pentagon to spend about $10 billion on buying 93 Lockheed Martin Co F-35 fighter jets, 14 more than the president's budget request, a congressional source said.

The bill also throws up a roadblock for Ligado Networks' low-power nationwide mobile broadband network because it would bar the Department of Defense from contracting with companies that use certain satellite communications frequencies, the source said. Ligado wants to tap the L-Band, which is also home to spectrum used by GPS systems, which are used by the military, businesses and consumers.

With Congress in session only until the end of the year, the House and Senate are running out of time to finalize the massive bill and avoid breaking the 59-year streak.

Section 230 of the Communications Decency Act protects tech companies from liability over content posted by users, and has been under attack from Trump and Republican lawmakers, who accuse internet platforms of stifling conservative voices.

White House spokeswoman Kayleigh McEnany said Trump was serious about his veto threat and wanted to use what leverage he had to repeal the tech protection law. "The president has made clear the importance of 230," she told a news briefing.

Trump, who lost his re-election bid to Democrat Joe Biden, is in his last weeks in office.

Steny Hoyer, the No. 2 House Democrat, called Trump's threat "shameless and indefensible." Trump and many of his supporters have been calling for the repeal of Section 230 since social media companies began removing or flagging material deemed to be inaccurate, frequently including tweets from Trump.

Republican House member Adam Kinzinger summed up the frustration of many with Trump with his own Tweet on Wednesday, noting how he would respond to a veto.

"I will vote to override. Because it's really not about you," Kinzinger wrote. (Reporting by Patricia Zengerle and Mike Stone, additional reporting by Richard Cowan and Andrea Shalal; Editing by Chris Sanders, Jonathan Oatis and Leslie Adler)