WASHINGTON (AP) --  A U.S. intelligence analyst who revealed the identities of four undercover agents to Cuban officials pleaded guilty Tuesday to espionage. She could spend 25 years in federal prison.

Ana Belen Montes, 45, was spying for Cuba from the time she started work at the Defense Intelligence Agency in 1985 until her arrest on Sept. 21, prosecutors say.

By that time, she was a senior intelligence analyst and had used short-wave radio and coded pager messages to give Cuba U.S. secrets so sensitive they could not be fully described in court documents.

"Yes, those statements are true and accurate," Montes told U.S. District Court Judge Ricardo Urbina after the charges were read.

When Urbina asked whether one reason she had agreed to plead guilty was "the fact that you committed the crime," Montes replied, "Yes."

Roscoe Howard Jr., U.S. attorney for the District of Columbia, said law enforcement officials did not know whether any of the information Montes transmitted to Cuba was shared with other countries. However, the Sept. 11 attacks on New York and Washington heightened the need to "get her off the streets," and influenced the timing of her arrest, he said.

Howard added that, to the government's knowledge, Montes received only nominal payments for expenses. He would not speculate on her motivation.

The four undercover agents whose identities she revealed, Howard said, are safe.

Under the plea agreement, Montes would accept a sentence of 25 years in prison with no possibility of parole, followed by five years of supervised release. In exchange, Howard said, the government would get her full cooperation in disclosing all information she may have about criminal activity regarding herself or others with whom she may worked. Urbina set a sentencing date for Sept. 24.

According to court papers, Montes communicated with the Cuban Intelligence Agency through encrypted messages and received her instructions over short-wave radio. The instructions were issued in numerical code, which she translated into Spanish text with a computer program provided by Cuba.

From public pay phones, she then used a prepaid calling card to send coded numeric messages to a pager owned by Cuban intelligence. Those messages, prosecutors said, typically were codes for "I received message" or "danger."

The FBI secretly searched Montes' residence under a court order on May 25 and uncovered information about several Defense Department issues, including a 1996 war games exercise conducted by the U.S. Atlantic Command, authorities said.

One of the messages the agents found suggested that Montes disclosed the upcoming arrival of a U.S. military intelligence officer in Cuba.

"We were waiting here for him with open arms," Cuban intelligence replied.

Another message from her Cuban contact said of the 1996 war games exercise: "Practically everything that takes place there will be of intelligence value. Let's see if it deals with contingency plans and specific targets in Cuba."

The DIA, based at Bolling Air Force Base in Washington, provides analyses of foreign countries' military capabilities and troop strengths for Pentagon planners.