With troop commitments growing, the cost of the war in Iraq could top $150 billion through the next fiscal year — as much as three times what the White House had originally estimated. And, according to congressional researchers and outside budget experts, the war and continuing occupation could total $300 billion over the next decade, making this one of the costliest military campaigns in modern times.

As a measure of the Bush administration’s priorities in the war on terrorism, it has spent about $3 in Iraq for every $1 committed to homeland security, experts say.

That divide may be growing.

The Pentagon says its monthly costs for Operation Iraqi Freedom shot up from $2.7 billion in November to nearly $7 billion in January, the last month for which ithas provided figures. Since then, the number of troops has jumped by 20,000 to 135,000, and the bloody insurgency has grown.

Defense officials initially said the troop increases were temporary, but last week they changed course and said they planned to maintain the higher levels through 2005, along with increased numbers of tanks and other heavy military equipment. The tempo of military operations has increased sharply in response to a wave of lethal attacks, suggesting the costs still may be climbing.

Both Democratic and Republican lawmakers have started to express deep concern over the costs and the way in which the Bush administration is choosing to cover them.

They contend that the White House has been relying on budgeting stratagems to conceal the overall expense, at least until after the election in November. And lawmakers worry that Congress is going to be forced to do something the White House has said until now was not necessary: Chop away at other government programs to cover the costs of an occupation that has no end in sight.

“DOD (Department of Defense) is being more than customarily opaque with us, ” Rep. John Spratt of South Carolina, the senior Democrat on the House Budget Committee, said in an interview. “We’re trying to pool our efforts and share information and piece something together, which is the only way to figure out what it is really going to cost us. But this is basic information. This is not unorthodox to get these numbers. It’s not asking for somebody to rework the whole books. I think they are embarrassed by the level of the costs.”

By contrast, Operation Desert Storm, begun in 1991 after Saddam Hussein’s armies invaded Kuwait, cost about $84 billion, adjusted for inflation, according to the Center for Strategic and Budgetary Assessments, a nonpartisan Washington think tank. But because the United States was part of a broad coalition of wealthy countries, including Britain, France, Germany, Japan and Saudi Arabia, about 90 percent of those costs were paid for by America’s allies.