The Federal Election Commission ruled Thursday that Sen. Scott Brown may use campaign funds to pay for activities related to the promotion of his autobiography. But the agency punted on his request that his publisher pay travel costs to events that both promote the book and raise funds for his campaign.

The FEC’s final advisory opinion, which was approved 4-2, allows the Massachusetts Republican’s campaign to purchase copies of the book, “Against All Odds.” Brown had asked the FEC in mid-January whether he could use campaign funds to buy several thousand copies of the book for campaign-related activities, including giving signed copies to large donors as gifts.

The opinion also allows him to promote the book on his campaign website and to rent out the campaign’s e-mail and mailing lists to sell the autobiography. His publisher, HarperCollins, would reimburse the campaign for the lists at fair market value.

But the opinion does not address Brown’s request to hold campaign events while on his book tour, for which HarperCollins is paying the travel expenses. The commission also could not agree whether Brown’s campaign may collect e-mail addresses from people attending the book tour’s events.

Brown, who won a 2009 special election to succeed the late Sen. Edward Kennedy (D), will face voters again for a full term in 2012. His campaign stated that he will either forgo royalties from the sale of the campaign-purchased books or donate the money to charity. Lawmakers and candidates are banned from tapping campaign funds for personal use.

The FEC opinion could have significant implications for lawmakers who moonlight as authors. According to a 2006 survey, 31 Senators in the 109th Congress, including then-Sen. Barack Obama (D-Ill.), had collectively written at least 74 books. Among current Senators, Joe Lieberman (I-Conn.) and Lamar Alexander (R-Tenn.) were tied on that list for the most books written, with six each.

Also Thursday, the FEC unanimously agreed that former Senate candidate Robin Carnahan (D) should be able to set up a legal expense fund to defend herself against a lawsuit brought by Fox News and the host of “Fox News Sunday,” Chris Wallace.

During her race in Missouri against then-Rep. Roy Blunt (R), Carnahan’s campaign aired a TV and Internet commercial in mid-September that included a clip of Wallace interviewing Blunt and asking some tough questions.

Fox and Wallace contend that the commercial infringes on Fox News’ copyright, invades Wallace’s privacy and “misappropriates his likeness,” according to Carnahan’s letter to the FEC.

Most requests for legal expense funds get approved by the FEC, but they are usually for Members of Congress or Congressional staff.