Months after the Armed Services committees drew up legislation directing a half-trillion dollars in national spending, the squeeze is on to pass the final authorization bill this session even as Congress is consumed with the nation’s crumbling economy.

The bill, approved by the House Wednesday, was brought to the floor under rules that barred amendments and limited debate. And that chafed Maryland Rep. Roscoe Bartlett and other Republicans, who wanted more time for such a vital bill.

“We’re spending not much time talking about half of all the money we spend,” Bartlett said, referring to the size of the defense budget relative to the nation’s total discretionary spending.

Still, the House and Senate Armed Services committees marked up their versions of the bill in May, giving lobbyists plenty of time to voice their opinions. And lobbyists, industry executives and members of Congress alike are hoping the legislation will squeak through before Congress adjourns for the fall campaigns.

Here’s a closer look:

Private security contracting

The bill scrapped a number of items that drew veto threats from President Bush and plenty of lobbying action.

One was a Senate measure tightening restrictions on how private security contractors operate in war zones — a direct reaction to an incident in which Blackwater Worldwide security guards, working in Iraq for the State Department, killed civilians the guards believed to be threats.

The bill before the Senate on Thursday instead takes up what the House recommended: an order for the government to better define “inherently governmental function.”

And that’s good news for the Professional Security Council, which more than tripled its advocacy budget this year, according to the Center for Responsive Politics.

The council was one of eight defense industry trade groups that make up the Acquisition Reform Working Group, which pressed Congress to dump the more restrictive measure, something Alan Chvotkin, executive vice president of the Professional Services Council, called “pretty stark policy.”

Missile defense

Lobbyists have tried, so far unsuccessfully, to lessen the blow of congressionally directed budget cuts to the Missile Defense Agency.

The bill would provide $10.1 billion for the Missile Defense Agency, a cut of $410 million from the president’s request.

Within that, advocates for the missile defense industry were closely watching the fate of funding for building missile defense sites in Poland and the Czech Republic. The bill provides $246 million less than the president sought, and missile defense advocates were hoping for more — especially in light of the recent conflict between Russia and Georgia.

The bill retains Senate language that requires the Pentagon to sign off on the system’s efficacy before it’s fully deployed.

Sen. Jeff Sessions (R-Ala.) said the European missile defense site is most important to him, “in the face of Russian pressure and bluster and pretty darn aggressive threats from Russia.”

“We definitely need to show that we’re committed to going forward with that,” Sessions said in an interview.

Air Force refueling tankers

Concern remains high in Alabama about the fate of a new competition for Air Force aerial refueling tankers. A contract was awarded to Northrop Grumman and the European Aeronautic Defence and Space Co., a team that planned to make tankers in Mobile, Ala., but the Pentagon is canceling the contract and plans to start a new competition next year.

The authorization bill dips into the new competition, requiring the defense secretary to do some trade policy research.

After the World Trade Organization, an international body known for operating at a glacial pace, rules on disputes over illegal subsidies for large commercial aircraft, the Pentagon has to review what effect the ruling would have on the tanker program.

The bill does not, however, require the Pentagon to wait for a WTO ruling before it awards a new contract in the ongoing battle between Boeing Co. and the Northrop Grumman-EADS team.

Coal-to-liquid fuel

Even when Congress is focused more than ever on alternative fuels, the coal industry couldn’t slip the energy provision it wanted into the $513 billion defense bill.

The Senate bill included a measure to allow the Defense Department to sign long-term contracts with the military for alternative fuels. But lawmakers backed off after the Congressional Budget Office priced the measure at an unexpected ­­$6 billion.

Approval of the measure would have been a big win in terms of securing financing to build plants that would refine coal into liquid fuel.

Sen. Robert C. Byrd (D-W.Va.) was such a big supporter of the bill that he asked Air Force Secretary Mike Donley to intervene in discussions on Capitol Hill.

Nevertheless, lawmakers settled on much less than what the coal industry sought. They ordering a Pentagon study on alternatives to reducing emissions from alternative fuels such as liquid fuel derived from coal.

Mike Wynne, the former Air Force secretary who asked Congress to include the measure, called this a “missed opportunity.”

Now it’s up to the Senate to pass the overall bill, but even the chairman of the Armed Services Committee has his doubts.

“Around the Senate, there’s always the possibility of a filibuster,” said Sen. Carl Levin (D-Mich.).

Even though Sessions has opposed items in the bill, he’s hoping it passes — sort of.

“We’ve passed the authorization bill for decades, and I don’t think we need to stop now, which is why it’s important to get the final wording correct,” he said.