But defense lawyers argued that wouldn't have been possible because the retired Air Force sergeant accused of spying for Iraq, Libya and China didn't have any information that would harm the U.S.
The two sides spelled out their cases at the start of Regan's espionage trial in Alexandria, Virginia.
The trial got under way, after months of procedural haggles, as 12 jurors and four alternates were seated. It is the first espionage case in 50 years that could lead to the death penalty.
Assistant U.S. Attorney Patricia Haynes charged that Regan, deeply in debt, was willing to offer classified information to America's enemies.
"This trial is about espionage," she said. "Espionage is a crime against the United States of America."
Defense attorney Jonathan Shapiro countered that Regan was playing spy and had no significant information to give to anybody.
"It may be a case of bad judgment bordering on stupidity," Shapiro said. "What Mr. Regan had with him was worthless. It wasn't even classified. It posed no harm to the United States."
Before beginning opening arguments, lawyers for both sides used more than half of their challenges as they selected the jury, which includes seven women.
Regan's trial is being held in the same federal courthouse where John Walker Lindh was sentenced to 20 years in prison last year for fighting with the Taliban militia in Afghanistan.
Regan is charged with three counts of attempted espionage and one of illegally gathering national security information. He has pleaded innocent.
It's rare for a spy case to go to trial. The government usually would rather cut a deal than run the risk of revealing in open court the ways it tracks spies.
The defense team and the U.S. attorney's office declined to comment on whether the government offered an out-of-court settlement.
CBSNews.com Legal Analyst Andrew Cohen says the defense must show that Regan did little national security damage.
"I don't know what Regan's attorneys will focus upon during the trial but if their client is convicted you can be sure during a penalty phase that the defense will remind jurors that admitted spies Robert Hanssen and Aldrich Ames are serving life sentences while Regan faces the possibility of the death penalty," said Cohen.
Information provided by the CIA's Ames and the FBI's Robert Hanssen led to the execution of U.S. agents overseas, but the government avoided a trial and agreed to plea bargains where both men were sentenced to life without parole.
If convicted, Regan could be the first American executed for spying since Julius and Ethel Rosenberg in June 1953. The Rosenbergs were convicted of conspiring to steal U.S. atomic secrets for the Soviet Union.
One of Regan's lawyers, Nina Ginsberg, has called the decision to seek the death penalty "disproportionate."
Regan retired from the Air Force in August 2000 to work for a defense contractor in the National Reconnaissance Office, which operates spy satellites.
A year later, FBI agents pulled Regan off a flight about to leave Washington for Zurich, Switzerland. They said he had a spiral notebook with codes describing images of a missile launcher in the northern no-fly zone over Iraq and of another launcher in China.
The FBI said Regan's home computer contained a letter to Saddam Hussein seeking $13 million in Swiss francs and offering information to help Iraq hide anti-aircraft missiles.
"I am willing to commit espionage against the United States by providing your country with highly classified information," the letter said, according to the indictment against Regan.
Court records indicate that Regan, a father of four, was $53,000 in debt.
Federal prosecutors said Regan's offer to sell information to Iraq put U.S. and allied pilots patrolling the no-fly zones there at "grave risk of death."
But defense lawyers claimed the letter was nothing more than "the alleged rantings of a retired Air Force master sergeant prepared in what appears to be an effort to scam a foreign government out of $13 million."
The trial before U.S. District Judge Gerald Bruce Lee likely will last about a month.