Federal Communications Commission Chairman Kevin Martin on Monday ordered a formal investigation into why two agency reports on media ownership were never made public.

Martin was responding to a request by Sen. Barbara Boxer, D-Calif., who earlier in the day made public a second FCC study that she says was shelved by agency officials.

Last week, Boxer released a draft of an FCC study that showed locally owned stations air more news than local stations controlled by outside owners. A lawyer with the FCC told The Associated Press last week that FCC managers ordered the destruction of that report; the lawyer is no longer with the agency.

"I want to assure you that I too am concerned about what happened to these two draft reports," Martin stated in a letter sent Monday evening to Boxer. "I have asked the inspector general of the FCC to conduct an investigation into what happened to these draft documents and will cooperate fully with him."

Martin added that he was not chairman at the time the reports were drafted, and that neither he nor his staff had seen them.

Boxer released the second report Monday afternoon. The FCC Media Bureau report analyzes the impact of deregulation in the radio industry. The report states that from March 1996 through March 2003, the number of commercial radio stations on the air rose 5.9 percent while the number of station owners fell 35 percent.

The intense concentration of ownership followed a 1996 rewrite of telecommunications law that eliminated a 40-station national ownership cap.

The report, apparently prepared in 2003, was never made public, nor have any similar analyses followed, despite the fact that radio industry reports were released in 1998, 2001 and 2002, Boxer said.

In a letter to Martin sent earlier Monday, the senator wrote, "This is the second report in a week that I have received that appears to have been shelved by officials within the FCC and I am growing more and more concerned at these developments."

Martin joined the commission in July 2001 and became chairman in March 2005. He stated he would order his staff to update the radio study and include it in the record of the commission's ongoing media ownership review.

In her letter, Boxer asked that the agency "examine whether it was then or is now the practice of the FCC to suppress facts that are contrary to a desired outcome."

In June 2003, the commission voted to loosen rules in virtually all areas of media ownership, including cross-ownership limits on radio and television stations. But commissioners at the time were also concerned about the emergence of radio giant Clear Channel Communications Inc., which now owns about 1,200 stations.

It decided to eliminate its existing system of measuring radio markets and use one favored by Arbitron, a private firm best known for measuring ratings. The commission decided not to force broadcasters to divest stations in markets where the new boundaries would push the broadcast companies over the limit.

Most of the rules the commission voted on in 2003 were thrown out by an appeals court in Philadelphia. The agency is reconsidering them. Clear Channel is lobbying the FCC to increase the number of stations that can be owned in the nation's largest markets.

Also on Monday, the FCC extended the period allowed for public comment on the ownership proceeding by a month, from Sept. 22 to Oct. 23. A public hearing is scheduled for Oct. 3 in Los Angeles.