WASHINGTON — Forced by law to reveal how much the nation spends on its spy agencies, the Bush administration disclosed Tuesday that the country's intelligence budget was $43.5 billion last year, an increase of about 50 percent since the Sept. 11, 2001, attacks.

The disclosure marked the first time in nearly a decade that the U.S. government has offered even a partial glimpse of how much it spends on the CIA and the other 15 agencies that make up the intelligence community. Only the overall figure was provided, without breakdowns.

The Bush administration had opposed releasing even that number, arguing doing so would give the nation's enemies valuable insight into how much money the United States was spending on clandestine activities.

But the release fulfills one of the recommendations of the commission that investigated the intelligence failures surrounding the Sept. 11 attacks. The commission urged the government to disclose the figure to foster greater public scrutiny of the nation's spending priorities. The recommendation was included in legislation passed by Congress earlier this year.

Steven Aftergood, director of the Project on Government Secrecy at the Federation of American Scientists, said releasing the figure is likely to demonstrate that basic information about the nation's spending on its spy programs can be shared without harming national security.

The information probably is of little use to adversaries trying to scrutinize U.S. intelligence activities, said Aftergood, whose organization unsuccessfully had sued the government to force release of the figure.

"What it does tell you is how much we're spending on intelligence compared to other government functions such as defense and health care," Aftergood said. "Also it makes it possible to openly debate the level of intelligence spending, something that has not been possible before in Congress."

But Director of National Intelligence J. Michael McConnell declined to provide further details on spy spending, saying there "will be no other disclosures of currently classified budget information because such disclosures could harm national security."

The government must disclose the comparable budget amount in 2008. But the intelligence director can block disclosure in subsequent years if he makes the case to Congress it is necessary to protect national security.

Some officials said the DNI's office might take that step because many intelligence officials believe that releasing numbers over a period of years would allow adversaries to examine trends in U.S. intelligence spending.

"If they see a blip, they can direct collection (by their own intelligence agencies) on what that blip might be," said a congressional official involved in classified intelligence budgets, speaking on condition of anonymity when discussing issues surrounding classified information.

The $43.5-billion figure is in line with independent estimates of the budget in recent years and represents the total spent during the fiscal year that began in October 2006 and ended Sept. 30 of this year.

The intelligence budget typically has been about 10 percent of military spending. Last year, the United States' defense budget was about $600 billion, including funding for the wars in Iraq and Afghanistan.

The figure represents spending on an array of intelligence activities, but the CIA and two other agencies account for the bulk of the budget. The others include the National Security Agency, which eavesdrops on phone calls and e-mails around the world, and the National Reconnaissance Office, which builds the spy satellites that orbit the Earth sending images and other data back to analysts on the ground.

NSA and NRO each might account for as much as $10 billion of the total, according to intelligence experts. The CIA's budget is believed to be between $5 billion and $8 billion annually.

The $43.5 billion does not include spending by the Army and other armed services on intelligence equipment and activities for military operations in the field, including the war zones of Iraq and Afghanistan.

Total spending on the nation's spy programs was disclosed voluntarily in 1997 and 1998 by then-CIA Director George J. Tenet. The figure for 1997 was $26.6 billion, and for 1998, it was $26.7 billion. But the numbers again were kept classified in succeeding years, although experts estimate the budgets probably approached $30 billion annually leading up to the Sept. 11 attacks.