WASHINGTON — In an apparent slip, a top U.S. intelligence official has revealed at a public conference what has long been secret: the amount of money the nation spends on its spy agencies.

At an intelligence conference in San Antonio last week, Mary Margaret Graham, a 27-year veteran of the CIA and now the deputy director of national intelligence for collection, said the annual intelligence budget was $44 billion.

The number was reported Monday in U.S. News & World Report, whose national security reporter, Kevin Whitelaw, was among the hundreds of people attending Graham's talk.

"I thought, 'I can't believe she said that,' " Whitelaw said on Monday. "The government has spent so much time and energy arguing that it needs to remain classified."

The figure itself comes as no great shock; most news reports in the past couple of years have estimated the budget at $40 billion. But the fact that Graham would say it in public is a surprise because the government has repeatedly gone to court to keep the current intelligence budget and even past budgets as far back as the 1940s from being disclosed.

Carl Kropf, a spokesman for the office of the director of national intelligence, John D. Negroponte, said Graham would not comment. Kropf declined to say whether the figure was accurate or whether her revelation was accidental.

Graham mentioned the number on Oct. 31 at an annual conference on intelligence gathered from satellite and other photographs.

Steven Aftergood, director of the Project on Government Secrecy at the Federation of American Scientists, expressed amused satisfaction that the budget figure had slipped out.

"It is ironic," Aftergood said. "We sued the CIA four times for this kind of information and lost. You can't get it through legal channels."

Only for a few past years has the budget been disclosed. After Aftergood's group first sued for the budget figure under the Freedom of Information Act in 1997, George J. Tenet, then the director of central intelligence, decided to make public that year's budget, $26.6 billion. The next year, Tenet did the same, revealing that the 1998 fiscal year budget was $26.7 billion.

But in 1999, Tenet reversed that policy, and budgets since then have remained classified with the support of the courts. Last year, a federal judge refused to order the CIA to release its budget totals for 1947 to 1970 — except for the 1963 budget, which Aftergood showed had already been revealed elsewhere.

In court and in response to inquiries, intelligence officials have argued that disclosing the total spying budget would create pressure to reveal more spending details, and that such revelations could aid the nation's adversaries.

That argument has been rejected by many members of Congress and outside experts, who note that most of the Defense Department budget is published in exhaustive detail without evident harm.

The national commission on the terrorist attacks of Sept. 11, 2001, recommended that both the overall intelligence budget and spending by individual agencies be made public "in order to combat the secrecy and complexity" it found was harming national security.

"The taxpayers deserve to know what they're spending for intelligence," said Lee H. Hamilton, the former congressman who was vice chairman of the commission.

Even more important, Hamilton said, public discussion of the total budgets of intelligence agencies will encourage Congress to exercise "robust oversight."

The debate over whether the intelligence budget should be secret dates at least to the 1970s, said Loch K. Johnson, an intelligence historian who worked for the Church Committee investigation of the intelligence agencies by the Senate in the mid-'70s.

Johnson said the real reason for secrecy might have less to do with protecting intelligence sources and methods than with protecting the bureaucracy.

"Maybe there's a fear that if the American people knew what was being spent on intelligence, they'd be even more upset at intelligence failures," Johnson said.