WASHINGTON (Bloomberg) - Warner Chilcott Ltd., maker of the Loestrin contraceptive, sued Barr Pharmaceuticals Inc. to block it from selling a generic version of the chewable birth-control pill, Femcon FE.

Barr filed an application with the US Food and Drug Administration in April to sell a low-cost version of the drug. As part of its application, Barr said it would not infringe the patent, or that it was invalid or unenforceable. The patent expires in 2019.

Warner Chilcott, based in Hamilton, Bermuda, began selling Femcon FE in the second half of 2006 and only began promoting the drug in April, the company said in August. Warner Chilcott called it the "top promotional priority" for its sales force. Femcon FE generated $11.5 million in sales in the first half of this year.

The lawsuit triggers an automatic 30-month period during which the FDA will not approve Barr's application, unless a court rules in Barr's favor before then.

Woodcliff Lake, New Jersey-based Barr makes the emergency contraceptive Plan B, also known as the morning-after pill. Generic oral contraceptives are its largest category of generic products. Spokeswoman Carol Cox did not immediately return a message seeking comment on the lawsuit.

Warner Chilcott fell 31 cents, or 1.7 percent, to $17.51 at 11.01am New York time in Nasdaq Stock Market composite trading, valuing the company at $4.4 billion. The stock is up 28 percent this year. Barr rose five cents to $54.22 in New York Stock Exchange composite trading, giving it a market value of $5.8bn. Barr stock is up eight percent in 2007.