During the Colorado stay, White completed a house sale in Aspen, raising questions as to whether he used the plane for personal business.
The inspector general, Joseph E. Schmitz, informed Defense Secretary Donald H. Rumsfeld's office that he is looking into the travel portion of Secretary White's affairs, said one official.
A second Pentagon official who confirmed the inspector general's investigation said it doesn't mean White did anything wrong. Both officials spoke on condition of anonymity.
White was made aware of the inspector general's intentions to conduct the investigation several days ago, an Army spokeswoman said.
"He will be cooperating with the investigative committee and he welcomes the investigation," said Col. Stephanie Hoehne.
During a meeting with reporters Wednesday, White said he had traveled with his wife on an Army plane to Colorado at the beginning of March. The plane they used was a Gulfstream jet, an Army version of those used by corporate executives, that costs between $1,200 an hour and $6,000 an hour to fly.
White said he was traveling outside Washington as part of the Bush administration's "continuity of government" plan, which requires some senior leaders to be outside the capital to ensure the government's survival should a major terror attack occur.
He said he also went to Dallas and Seattle on official Army business during the trip and Colorado was a convenient weekend stopover in between.
"I had to be in Seattle on Monday for meeting with Microsoft. I had official duties in Dallas on Friday. And if you draw a straight line between Dallas and Seattle, it probably crosses over Colorado, so that's the way I did it," White said.
White also has been the subject of attention in connection with his sale of Enron Corp. stock after taking over as the Army's top civilian.
In his first extensive comments on the matter, White said Wednesday he would resign if the investigation into the bankruptcy of his former employer, Enron, distracts him too much from his military duties.
A top Enron executive until he took over as Army secretary last May, White denied any wrongdoing in his dealings with the company. He said he was as surprised as the rest of the country by the energy trading company's collapse in December, and the subsequent allegations of massive fraud.
White said he has sold all of his interests in Enron, as required by his Army post.
He said he remains part of an annuity fund for Enron retirees. However, that fund has not paid any money since Enron's collapse, and he has joined other retirees in filing a claim in the company's bankruptcy.
He said he is turning over "a bunch" of military and personal documents relating to Enron to the Defense Department, which will supply them to the Justice Department investigation.
White's critics have said they want to know whether his conversations with Enron officials prompted him to finish his stock sales quickly, before Enron's shares hit bottom. Enron's stock hit a low of 26 cents by the end of November, White's deadline to sell.
White made about $12 million from selling his Enron shares, the last of which he sold Oct. 30 at $12.86 a share.