The Homeland Security Department has launched an internal investigation into whether department officials privately tipped off relatives or friends about last week's subway terrorism threat before the public learned of the news, officials said Thursday.

The probe was announced just as Gov. George Pataki and Police Commissioner Raymond Kelly raised concerns about the possible leak, first reported in the Daily News.

"Obviously it's disturbing; it's just not right," Gov. George Pataki said after presiding over a midtown Manhattan ceremony honoring two police detectives killed in the line of duty. "The public should know at the same time."

Police Commissioner Raymond Kelly (search), who attended the ceremony, afterward confirmed a report in Thursday's editions of the Daily News that police had obtained copies of personal e-mails that alluded to an alleged Al Qaeda plot, and had forwarded them to federal officials.

A Homeland Security spokesman in Washington, Russ Knocke, said that an internal investigation was under way.

"We take any potential leak of sensitive or classified information very seriously," Knocke said.

When FBI and police officials went public with the threat on Oct. 6, Homeland Security downplayed it, saying it was "of doubtful credibility." After four days of high alert, local officials announced Monday there was no clear evidence an attack would be carried out and scaled back the protection.

"It's ironic that on the one hand the department is saying this is not a credible threat and then, if these e-mails are true, people within the department with access to classified information felt it was worth contacting their own families," said Rep. Peter King, R-N.Y., chair of the House Homeland Security Committee.

The e-mails began circulating on Oct. 3 — three days before Kelly and Mayor Michael Bloomberg announced they were putting thousands of extra police officers on patrol in the subways in response to the possible plot to bomb the subway (search) using briefcases or baby strollers packed with explosives.

The Daily News story quotes one e-mail — purportedly penned by the unnamed son of a high-ranking Homeland Security official — in which he warns the recipients, "The only information I can pass on to you is that everyone should at all costs not ride the subway for the next two weeks in major areas of NYC."

In another e-mail, the writer describes receiving "a most disturbing call" from the Coast Guard's liaison to Homeland Security who relayed "a very specific warning to not enter the New York City subway system from Oct. 7 through Oct. 10."

Asked about the e-mails, Pataki said, "There should not be limited public notification to a handful of people, or people who might be otherwise politically connected."

Kelly called for an investigation to determine "if, in fact, this is inside information that's being put out by a public official."