Hi-tech fighter aircraft, new warships and missile defense projects are all potential targets for big cuts in the US defense budget, as the American military faces a new era of limits under President Barack Obama.

With a mushrooming budget deficit of more than a trillion dollars, the new administration has signaled it hopes to scale back military spending partly through a planned reduction of troops in Iraq and by taking the axe to big ticket weapons programs.

"It's easier to cut weapons than personnel," said Loren Thompson of the Lexington Institute.

"There are clear signs that US defense spending peaked in 2008 and that it will be gradually declining over the next four years as the United States reduces its presence in Iraq," Thompson told AFP.

Obama's predecessor signed a 612 billion dollar defense authorization bill in September, the largest in real terms since World War II. But the economic crisis means defense spending will come under more pressure and restrictions.

In his speech to Congress on Tuesday, Obama promised his upcoming budget would bolster the pay and benefits of soldiers and increase the total number of troops but that unnecessary, "Cold War-era" weapons would be dumped.

Defense Secretary Robert Gates, placing a top priority on fighting insurgents rather than conventional warfare, has warned that big weapons projects plagued by delays and cost overruns will come in for tougher scrutiny.

A list of candidates for possible cutbacks drawn up by the Pentagon includes more Navy destroyers built by General Dynamics, fighter jets including Lockheed Martin and Boeing's F-22 Raptors and carrier-based Super Hornets, a digital radio system for all the armed services and missile defense weaponry for Poland and the Czech Republic.

Gates has already singled out the F-22 Raptor fighters, which cost about 350 million dollars each, for potential cutbacks.

Military analysts have also questioned the need for more Navy aircraft carriers and a computer-linked network of Army vehicles, known as Future Combat Systems, which has faced criticism.

Gates has expressed frustration at slow-moving weapons programs that seem unrelated to the immediate threats posed by militants in the rugged mountains of Afghanistan or the deserts of Iraq.

The United States cannot "eliminate national-security risks through higher defense budgets, to do everything and buy everything," Gates wrote recently in the journal Foreign Affairs.

But lawmakers in Congress, many of whom receive campaign funding from military contractors, have a long tradition of fending off cuts to weapons projects in their home districts.

Determined to stem leaks over budget questions, Gates has made senior officials promise they will keep the details of defense budget talks secret as his department prepares to make tough cuts, a spokesman said.

In an unprecedented move, Gates has asked top military officers and civilian officials to sign non-disclosure forms in which they agree not to reveal deliberations about the politically charged budget.

"This is highly sensitive stuff involving programs costing tens of billions of dollars, employing hundreds of thousands of people and -- and go to the heart of national security," press secretary Geoff Morrell said.

Some conservative analysts argue constraints on defense spending could mean the United States will over time lose its strategic dominance as other countries seize on possible weaknesses.

"When you step back from all the details and look at what is really happening in the new administration, American military power is likely to decline in the years ahead due to a lack of money," Thompson said.

On the political left, Obama has already been accused of failing to rein in the vast Pentagon budget that represents nearly half of the world's military spending.

"The Barack Obama administration is continuing the neo-conservative agenda of US military domination of the world -- albeit with perhaps with a kinder-gentler face," said Peter Phillips, a professor at Sonoma State University and director of Project Censored.