WASHINGTON, March 23 (Reuters) - A U.S. judge on Friday refused to grant a preliminary injunction AstraZeneca sought to delay the market entry of generic versions of its top-selling anti-psychotic drug Seroquel, saying the company failed to make a clear showing that it was entitled to one.

The London-headquartered pharmaceutical company earlier this month sought an injunction to bar the U.S. Food and Drug Administration from granting final marketing approval of generic forms of Seroquel until December 2012.

"Because the court finds that AstraZeneca has failed to make a clear showing that it is entitled to the extraordinary remedy of a preliminary injunction, its application shall be denied," U.S. District Judge Judge Colleen Kollar-Kotelly wrote in a 33-page decision.

The company failed to prove that it would succeed in its court battle to extend its exclusivity for the drug or that the economic harm it described as a result of the generic versions was likely, the judge said.

A spokesman for AstraZeneca was not immediately available for comment.

Generic copies of the original instant-release form of Seroquel are due to hit the U.S. market on March 26 when AstraZeneca's patent expires - an event that will have a significant impact on both sales and profits.

AstraZeneca is currently budgeting for a 2012 revenue fall at the group level of more than 10 percent, in large part as a result of loss of exclusivity on Seroquel in both the United States and Europe.

The case is AstraZeneca Pharmaceuticals LP v Food and Drug Administration et al in U.S. District Court for the District of Columbia, No. 12-cv-388.

For AstraZeneca: Timothy Hester of Covington and Burling.

For the FDA: Gerald Kell of the U.S. Department of Justice.

(Reporting by Jeremy Pelofsky; additional reporting by Ben Hirschler)

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