NEW YORK (AP) – Rupert Murdoch is stepping up his campaign to woo the controlling shareholders of Dow Jones & Co., the Bancroft family, promising them a board seat on his media conglomerate, News Corp., as well as measures to ensure the independence of The Wall Street Journal.

Mr. Murdoch, in a letter to the Bancroft family dated May 11, promised to set up an independent editorial board for the Journal, as he did with The Times of London, which would arbitrate any disputes between the editors and management. The board would also have to sign off on any decision to hire or fire the top two editors at the paper.

The Journal reported news of Murdoch’s overture to the Bancrofts on Monday on its Web site and posted a text of the letter, which News Corp. spokesman Andrew Butcher confirmed to be accurate. A spokesman for the Bancroft family declined to comment.

Mr. Murdoch first approached Dow Jones on March 29, and news of his subsequent offer became public on May 1. Since then, the Bancroft family, which controls the company’s shareholder vote through a special class of shares, has said they are opposed to Murdoch’s bid.

However, the Bancrofts have not rejected Mr. Murdoch’s bid outright and are not unanimous in their opposition, having lined up only 52 percent of the shareholder vote against him, short of the 64 percent voting block they control. About 80 percent of the family are opposed to the bid.

The union representing Journal employees has also voiced strong opposition to Mr. Murdoch’s offer, saying they fear he would “crush quality and independence” at the paper, and another significant stockholder, Jim Ottaway Jr., has said he opposes ownership by Murdoch. Ottaway controls about 5 percent of Dow Jones’ vote.

Mr. Murdoch assures the Bancroft family in his letter that “first and foremost, I am a newspaper man. I don’t apologize for the fact that I have always had strong opinions and strong ideas about newspapers; but I have also always respected the independence and integrity of the news organizations with which I am associated.”

Mr. Murdoch said the Journal represented “American journalism at its best. … Any interference – or even hint of interference – would break the trust that exists between the paper and its readers, something I am unwilling to countenance.”

Dow Jones correspondent Clarence Barron bought control of the company in 1902, and his stake passed to Jane Barron, the daughter of his wife, Jessie Waldron. Jane Barron married Hugh Bancroft, and their stake in Dow Jones has been passed to their descendants. The Journal reported on Saturday that there are now more than 20 trusts holding the Bancroft family’s stake.

One thing Mr. Murdoch didn’t do in his letter was to raise his offer for Dow Jones, which is currently $60 a share, valuing the company at $5 billion.

The offer represents a huge premium of more than 65 percent over Dow Jones’ share price before the bid became public, and the stock has jumped since then to approach the level of Mr. Murdoch’s offer. The shares rose 67 cents Monday, or 1.3 percent, to $53.77.

Mr. Murdoch said in his letter that he would like to use News Corp.’s considerable global resources to expand Dow Jones’ operations overseas as well as the Journal’s Washington coverage, and also to upgrade Dow Jones’ headquarters facilities in New York.

Mr. Murdoch, whose company owns Fox News Channel, the New York Post and newspapers in England and Australia as well as MySpace and Twentieth Century Fox, has said he hopes to use the Journal’s resources to help launch a business-themed cable news network later this year, to rival General Electric Co.’s CNBC.