WASHINGTON — Prosecutors contend that a former State Department official at the center of an espionage investigation, Donald Keyser, urged Taiwanese intelligence agents to recruit a Heritage Foundation Asia employee as a spy.

Keyser identified a senior research fellow at the conservative think tank, John Tkacik Jr., as “ripe for recruitment” in a May 2004 e-mail to a Taiwanese intelligence agent with whom Keyser had an intimate relationship, Isabelle Cheng, according to court records obtained byThe New York Sun.

In an interview yesterday, Mr. Tkacik, who headed the China section of the State Department’s Bureau of Intelligence and Research, said he was outraged at Keyser’s actions.

“The fact that I was named by a colleague suggesting that I was somebody that they should be going after as a recruitment target, that’s just sickening,” Mr. Tkacik said. “I fervently hope they throw the book at him.”

Keyser, a 30-year veteran of the foreign service who was one of the State Department’s top Asia hands, pleaded guilty in December to storing thousands of classified documents at his home and lying about his contacts with Ms. Cheng.

In June, the government asked to be released from the plea bargain on the grounds that Keyser has been less than candid in recent debriefings. If Judge Thomas Ellis III grants the motion, Justice Department attorneys have indicated that they may bring espionage charges against Keyser.

Keyser’s attorneys assert that he has been fully cooperative and that he has conceded “that there was a sexual component to his relationship with Ms. Cheng.” However, the defense attorneys claim that the FBI wants Keyser to admit to turning over classified information to his paramour when he only disclosed information cleared for release to Taiwan.

In the May 2004 e-mail to Ms. Cheng, Keyser disparaged Mr. Tkacik as a disgruntled individual who “spent a career in the foreign service not being taken seriously.”

“This is the kind of person who is ripe for recruitment by careful, methodical, serious intelligence agencies.In the days of the Cold War, Soviet and East German intelligence officers were quite practiced at identifying people like this, people who did not wake up one day and say, ‘I want to be a traitor,’ but people whose relatively minor weaknesses and ego gratification needs made them potential targets,” Keyser wrote.

In a letter filed with the court, an attorney for Keyser, Robert Litt, disputed the government’s view. “Mr. Keyser never suggested any candidates for recruitment,” Mr. Litt wrote.

He said Keyser simply was trying to undercut Mr. Tkacik’s credibility because of attacks the Heritage scholar had mounted on America’s de facto ambassador to Taiwan at the time, Douglas Paal. In a March 2004 e-mail filed with the court, Keyser alerted Mr. Paal that Mr. Tkacik was circulating speculation that the American envoy urged the State Department not to express concern about an apparent assassination attempt against President Chen of Taiwan. “Da Boyz are trying to stir things up,” Keyser wrote.

Mr. Litt said Keyser believed “that Mr. Tkacik was already, in effect, on the payroll of certain factions in Taiwan and was attempting to undermine Mr. Paal’s authority as an official representative” of the American government.

Prosecutors have termed the defense explanation “not credible.” However, Mr. Tkacik said yesterday that no one from the Taiwanese government approached him about becoming an agent and the FBI never contacted him to see if any such approach had been attempted. “No one has come to me,” he said.

The Heritage scholar said funding of his work is arranged by development officials. “As far as I’m concerned, I’m not on anybody’s payroll except the Heritage Foundation,” he said. Foundation officials could not be reached for comment.

Mr. Tkacik confirmed yesterday that while in Taiwan in 2004 he sent an email to a so-called “listserv” of China watchers describing Mr. Paal’s alleged slow-walking of the official American response to the assassination attempt, which many Taiwanese viewed as staged. However, Mr. Tkacik said he made clear at the time that he had no firsthand knowledge of Mr. Paal’s alleged actions.

Efforts to contact Mr. Paal, who is now an executive with JPMorgan Chase International, were unsuccessful.

While Mr. Tkacik’s name was redacted from some court filings by the government and the defense, the Heritage scholar was identified twice by name in a letter filed in June as part of a defense pleading. In addition, references to Mr. Tkacik’s background in an e-mail filed by both sides in the case made his identity evident to those familiar with leading experts on relations among America, Taiwan, and communist China.

Before the government moved to bring new charges, three former American ambassadors to China — James Lilley, Winston Lord, and J. Stapleton Roy, as well as dozens of other diplomats and ex-diplomats — submitted letters arguing against jail time for Keyser. Some said he had saved the lives of several Chinese dissidents, among them a prominent labor activist, Harry Wu.