WASHINGTON (Reuters) - The powerful head of the House of Representatives subcommittee that controls the purse strings of the Pentagon said on Wednesday he was troubled by ebbing support for defense from fellow lawmakers.

Representative John Murtha, chairman of the defense subcommittee of the House Appropriations Committee, said defense spending was clearly going to decline in coming years, but the country faced new threats that needed to be addressed.

He cited waning support for defense among U.S. lawmakers, saying the recent fiscal 2009 war spending bill nearly failed but for the strong intervention by House Speaker Nancy Pelosi.

“Defense is going to start to go down. The public has lost interest,” the Democrat from Pennsylvania said.

“You’re going to see a change, a sea change. I’m surprised myself at how little interest there is in what’s going on in Iraq and Afghanistan, and yet we’ve got troops deployed.”

Democrats could even refuse to fund war bills if the Obama administration failed to make good on its promise to withdraw U.S. troops from Iraq, Murtha said. “It’s quite possible that we could lose the war funding. If it hadn’t been for the speaker, we would have lost it this time.”

The U.S. House narrowly passed the $106-billion bill to pay for the Iraq and Afghanistan wars, with the measure garnering only five Republican votes and 32 Democrats voting against it.

Murtha said he met with Defense Secretary Robert Gates on Tuesday and the two men agreed that the biggest threat to the United States was the growing Taliban influence in Pakistan.

“Gates and I both agree that Pakistan is the biggest single threat to the United States. Why? Because there’s nuclear weapons there and the country’s not stable. We don’t know what might happen in Pakistan,” Murtha said.

Murtha said he would strongly advise U.S. intervention in Pakistan if the Taliban seized power, and said the U.S. government already had contingency plans to “destabilize” sites in Pakistan believed to house Taliban weapon stores.

Murtha questioned President Barack Obama’s plan to increase the number of troops in Afghanistan, and said it was imperative for the U.S. military there to avoid the level of civilian casualties seen in Iraq because of a possible backlash.

“Killing civilians in Afghanistan is the worst thing we could do,” Murtha said. “They could turn against us.”

Murtha also expressed concerns about potential conflicts in the future with China over world energy supplies, and said it would be good to have Japan operating its own F-22 fighter jets, if that became an issue.

Lawmakers are considering lifting a ban on exports of the F-22, the top U.S. air superiority fighter built by Lockheed Martin Corp, to allow Japan to buy 40 to 60 planes.

He questioned the administration’s decision to halt production of the F-22 and said he was considering a measure to add funding for 20 more planes to the fiscal 2010 budget, especially given current maintenance issues with the fighter.

Much would depend, he said, on independent threat assessments, as well as news about the F-35 Joint Strike Fighter program, also run by Lockheed.

He said there was some support in the House, but not by a majority, for extending the F-22 production line. In the end, he said, it could prove difficult to find the $3.2 billion needed to pay for 20 more planes in the fiscal 2010 budget.

Murtha predicted funding would be added for Boeing Co-built F/A-18s to bridge the Navy’s expected shortfall of strike fighters, but said details were still being worked out.

“If we don’t build F-22s, and the maintenance problems continue to be as severe as they are, that means we wouldn’t have F-22s available if something happened,” he said, noting that maintenance costs currently amounted to $50,000 an hour.

Any exports would begin only in two to three years, and their cost would rise sharply if U.S. production ended before that, Murtha said.

He also cited developmental problems with the F-35, and said the House might not fund all 30 planes sought by the Pentagon in fiscal 2010, at least until the plane had come further through the testing process.