WASHINGTON — The head of Delta Air Lines on Friday joined the growing opposition to the Transportation Security Administration's new policy allowing passengers to carry small knives onto planes. Delta chief executive officer Richard Anderson said in a letter to TSA Administrator John Pistole that he shares the "legitimate concerns" of the airline's flight attendants about the new policy. Allowing small knives to be carried on board after a ban following the Sept. 11, 2001, attacks "will add little value to the customer security process flow in relation to the additional risk for our cabin staff and customers," Anderson said in the letter, which was obtained by the Associated Press. Delta, based in Atlanta, is the world's second-largest airline. It is the first major airline to join not only flight attendants but pilots, federal air marshals and insurance companies in a burgeoning backlash to the policy. Pistole announced the policy on Tuesday. TSA spokesman David Castelveter declined to comment on the letter. He said TSA plans to implement the policy on April 25 as scheduled.Anderson cited only small knives in his letter. The policy will also allow passengers to include in their carry-on luggage novelty-size baseball bats less than 24 inches long, toy plastic bats, billiard cues, ski poles, hockey sticks, lacrosse sticks and two golf clubs. Items such as box cutters and razor blades will still be prohibited.Knives permitted under the policy must be able to fold up and have blades 2.36 inches or less in length and less than ½ inch in width. The policy is aimed at allowing passengers to carry pen knives, corkscrews with small blades and other small knives.