A criminal investigation is under way into the airline travel of President Bush's former education secretary, adding to the controversy for the White House on travel by top government aides, officials said Friday.

Disclosure of the investigation into the travel practices of Lauro Cavazos, who resigned the Cabinet post last December, follows a controversy over White House chief of staff John Sununu's use of military aircraft.The investigation of Cavazos - which began in mid-1990 while he was still education secretary - is being conducted by the Education Department and the Justice Department, the officials said.

No mention of the probe was made when Cavazos resigned.

It was widely reported at the time that Bush was unhappy with Cavazos' performance and that he had failed to help Bush carry out his campaign pledge to be the "education president."

The officials confirmed that the investigation covered whether Cavazos used frequent-flier credits from official travel to obtain free tickets for his wife to accompany him. He had been told that his wife could not accompany him on trips at government expense.

Government regulations require federal employees must turn over all such frequent-flier travel bonuses to the government.

Bush Thursday issued a new policy that partially bans Sununu from using military planes at taxpayer expense in order to avoid any appearance of impropriety.

In a revamped policy, Bush ordered his aide to submit requests to fly on military aircraft to the White House legal counsel for approval.

He also prohibited Sununu from taking government planes for political travel unless there is also an important official reason or unless Bush himself gave the nod.

Ironically, it was Sununu who was instrumental in demanding that Cavazos resign.

It is highly unusual for a criminal probe to involve a current or former Cabinet official.

The officials were unable to say how much longer the investigation would last, how many trips were under scrutiny and how much money might be involved.

A Justice Department spokesman for the criminal division, Doug Tillett, had no comment.

The investigation was disclosed in an article by the New York newspaper Newsday Friday and confirmed by the officials, who are involved in the investigation and asked not to be named.

Newsday said Cavazos and his wife would travel on TWA as often as possible, even though it often required complicated and time-consuming routes to make connections. His wife could go free on TWA because one of their sons worked for the airline as a pilot, it said.

The officials declined to discuss particulars of the investigation, saying only that it was "airline-travel related."

An Education Department spokesman said Friday, "So far as I know, no one here is in any kind of contact with him."

Asked where Cavazos went to work, he said, "We have not heard of anything."

Cavazos, a former professor and administrator at Texas Tech University in Lubbock, Texas, and Tufts University in Boston, was appointed by President Ronald Reagan in 1988 and kept in office by Bush.