Here’s the best thing that can be said about the new detention powers the Senate has tucked into next year’s defense bill: They don’t force the military to detain American citizens indefinitely without a trial. They just let the military do that. And even though the leaders of the military and the spy community have said they want no such power, the Senate is poised to pass its bill as early as tonight.

There are still changes swirling around the Senate, but this looks like the basic shape of the 2012 National Defense Authorization Act. Someone the government says is “a member of, or part of, al-Qaida or an associated force” can be held in military custody “without trial until the end of the hostilities authorized by the Authorization for Use of Military Force.” Those hostilities are currently scheduled to end the Wednesday after never. The move would shut down criminal trials for terror suspects.

But far more dramatically, the detention mandate to use indefinite military detention in terrorism cases isn’t limited to foreigners. It’s confusing, because two different sections of the bill seem to contradict each other, but in the judgment of the University of Texas’ Robert Chesney — a nonpartisan authority on military detention — “U.S. citizens are included in the grant of detention authority.”

An amendment that would limit military detentions to people captured overseas failed on Thursday afternoon. The Senate soundly defeated a measure to strip out all the detention provisions on Tuesday.

So despite the Sixth Amendment’s guarantee of a right to trial, the Senate bill would let the government lock up any citizen it swears is a terrorist, without the burden of proving its case to an independent judge, and for the lifespan of an amorphous war that conceivably will never end. And because the Senate is using the bill that authorizes funding for the military as its vehicle for this dramatic constitutional claim, it’s pretty likely to pass.

It would be one thing if the military was clamoring for the authority to become the nation’s jailer. But to the contrary: Defense Secretary Leon Panetta opposes the maneuver. So does CIA Director David Petraeus, who usually commands deference from senators in both parties. Pretty much every security official has lined up against the Senate detention provisions, from Director of National Intelligence James Clapper to FBI Director Robert Mueller, who worry that they’ll get in the way of FBI investigations of domestic terrorists. President Obama has promised to veto the bill.

Which is ironic. After all, Obama approved of the execution without trial of Anwar al-Awlaki, al-Qaida’s YouTube preacher, based entirely on the unproven assertion that Awlaki was dangerous. Awlaki was an American citizen. So Obama thinks he has the right to kill Americans the government says are terrorists, but he doesn’t want the military to lock them up forever without trial. OK then.

Weirder still, the bill’s chief architect, Sen. Carl Levin (D-Mich.), tried to persuade skeptics that the bill wasn’t so bad. His pitch? “The requirement to detain a person in military custody under this section does not extend to citizens of the United States,” he said on the Senate floor on Monday. The bill would just let the government detain a citizen in military custody, not force it to do that. Reassured yet?

Civil libertarians aren’t. Sen. Al Franken (D-Minn.) said it “denigrates the very foundations of this country.” Sen. Rand Paul (R-Ky.) added, “it puts every single American citizen at risk.”

But there’s a reason this measure goes into the defense bill: Voting against the defense bill is usually considered political suicide. That’s why the bill will almost certainly pass tonight. If Obama backs down from his veto threat, get ready to see Americans at Guantanamo Bay.

Photo: U.S. Army