The FBI's handling of confidential informants should be a key part of Senate hearings into the arrests on spying charges of a former FBI counterintelligence agent and an alleged Chinese double-agent, three senior senators say.

"We believe that it is incumbent on the Judiciary Committee to examine whether there are larger security issues that continue to persist," said a letter signed by Sens. Patrick Leahy, D-Vt. (search), Charles Grassley, R-Iowa (search), and Arlen Specter, R-Pa. (search)

The letter to Judiciary Committee Chairman Orrin Hatch (search) requests hearings as soon as possible into the case of former FBI agent James J. Smith and Katrina Leung, a Los Angeles businesswoman and socialite who is accused of being a Chinese double agent -- and also Smith's longtime lover.

Smith is free on bond; Leung has been jailed without bond since the two were arrested April 9.

The letter released Monday said the Leung case, as well as the FBI's handling of informants in the Boston case of fugitive mobster James "Whitey" Bulger, underscore "long-standing concern" about FBI dealings with informants.

In the Boston case, former FBI agent John Connolly is serving a 10-year prison sentence for protecting Bulger and another crime kingpin. While senior FBI officials have portrayed Connolly and several colleagues as rogue agents, there were also at least 26 memos written between the Boston field office and FBI headquarters indicating top officials knew what was going on.

It remains unclear exactly how much officials at FBI headquarters knew about Smith and Leung, who is accused of passing classified information she took from Smith to the People's Republic of China. Leung was Smith's intelligence asset for 18 years, during which time the two also had a sexual relationship, prosecutors say.

"If even a portion of the allegations raised in the public affidavit are true, we cannot afford to wait until yet another breach of national security occurs before we work with the FBI to improve security and the handling of confidential informants," the senators' letter says.

A spokeswoman for Hatch, a Utah Republican, did not immediately return a telephone call seeking reaction.

Sen. Joseph Lieberman, D-Conn. (search), also has asked for a Justice Department and FBI investigation. He wants to know whether any of Leung's contributions to Republican campaigns came from the Chinese government.

Lieberman's Republican-controlled committee conducted an investigation in 1997 into whether Chinese government officials tried to influence the 1996 election with donations to Democratic candidates. The committee's findings were inconclusive.