The Washington Post Co. announced yesterday that Board Chairman Katharine Graham, members of her family and trustees for several family trusts have converted 305,378 of their class A shares in the communications firm into an equal number of class B common stock.

Graham, family members and trusts own all class A common stock, which is the controlling ownership vehicle. Class B stock is listed on the American Stock Exchange and is traded publicly, with class B owners electing a minority of the company's board of directors.

According to a company statement, the transaction took place Last Friday. The purpose of the conversion is to increase the number of class B shares owned by the Graham family and family trusts "in order to facilitate financial planning," the statement added.

For example, class B shares could be traded publicly in the future, providing a flexibility impossible with stock for which there is no public market. Such shares also could be used in charitable contributions because there would be a specific public market value.

Because all class A stockholders converted the same percentage of their shares, the conversion does not change their proportionate holdings of class A stock, and Graham continues to vote the majority of that class.

With the conversion completed, the company has 2.75 million shares of class A shares outstanding, all owned by the Graham family or family trusts, and 11.22 million shares of class B shares, of which the Graham family and family trusts own about 700,000 shares.