The Pentagon budget for next year is dishonest and generals who have endorsed it on Capitol Hill are not giving Congress their true advice, a senior Republican lawmaker on budget matters said on Thursday amid rising rhetoric over looming defense cuts.

Representative Paul Ryan, head of the budget committee of the House of Representatives, said the defense budget President Barack Obama sent to Congress last month was driven by spending constraints and not by the new U.S. military strategy unveiled in January.

We don't think the generals are giving us their true advice. We don't think the generals believe that their budget is really the right budget, Ryan told a forum sponsored by the National Journal magazine hours before his own budget plan passed the House.

He said the Pentagon's new U.S. defense strategy calls for a shift to the Pacific, a move that means you need a Navy and Air Force that can extend its reach into those areas.

This budget doesn't do that. So I think the strategy doesn't match the budget because I think what is going on here is this is a budget-driven strategy not a strategy-driven budget, Ryan said, adding that the spending plan was not really a true, honest and accurate budget.

Top defense officials who testify before Congress are sworn to give their best military advice and the uniformed and civilian leaders of all four services have testified repeatedly on the budget in recent weeks.

Pentagon Press Secretary George Little, reacting to Ryan's comments, said Defense Secretary Leon Panetta expects honest, straightforward input from our military leadership and he believes that's precisely what they do on a regular basis, time and time again.

A spokesman for Ryan seemed to backtrack later, saying the congressman believes the integrity of our generals and admirals is unimpeachable.

The top Democrat on the House Armed Services Committee told an audience at the Rand corporation think tank he thought the debate over whether the strategy was driven by the budget was endless and to my mind ridiculous.

The clear implication is that any strategy that is driven by a budget is somehow ... heretical. How dare you put our national security on a budget? That strikes me as insane because every decision that we all make is driven in part by the budget, said Representative Adam Smith.

HOW DEEP TO CUT?

Top uniformed officers who have testified to Congress have endorsed Pentagon plans to cut back on projected military spending by $487 billion over the next decade as the United States winds down the wars in Iraq and Afghanistan.

But they have warned against a further $500 billion in cuts that could go into effect next year unless Congress takes action to stop them. The cuts are part of efforts by Obama and Congress to end an era of trillion-dollar budget deficits.

The Pentagon said on Thursday it expected hundreds of thousands of layoffs across the defense industry if lawmakers did not take action to avert the looming $500 billion in defense budget cuts.

Frank Kendall, the Defense Department's acting undersecretary for acquisition, technology and logistics, said the cuts would force the Pentagon to break many hard-won contracts with industry, including a multibillion dollar deal with Boeing Co for development of a new refueling plane.

The Navy's contracts with Lockheed Martin Corp and Australia's Austal Ltd for littoral combat ships would also be vulnerable if the mandatory cuts, known as sequestration, took effect as planned, Kendall told the Senate Armed Services Committee at his confirmation hearing.

A lot of the work that we've done over the last couple of years to try to make more efficient acquisition decisions and get better contract structures would be broken, he said.

Kendall said the cuts would ripple through all tiers of the defense industry, hitting small and medium-sized businesses particularly hard.

He said some of the biggest companies in the sector had already approached him with concerns about having to provide advance notice of potential layoffs given the uncertainty caused by the current budget situation.

Smith, who appealed for Congress to stop fighting every proposed cut and deal realistically with the U.S. deficit, said uncertainty over additional defense cuts next year and the expiration of the Bush tax cuts was suppressing job growth.

The uncertainty of all this is almost as bad as the reality, he said. Businesses out there are not hiring people. They're laying people off because they don't know whether Congress will act in time.

(Additional reporting by Donna Smith; editing by Gerald E. McCormick and Todd Eastham)