WASHINGTON (Reuters) - The U.S. Patent and Trademark Office said on Tuesday it would appeal a court decision that threw out agency rules aimed at limiting the size of patent applications and reducing a backlog of patent applications.

Judge James Cacheris of the U.S. District Court for the Eastern District of Virginia tossed out the rules on April 1, saying they exceeded the patent office's rulemaking authority.

The ruling was a victory for Europe's biggest drugmaker, GlaxoSmithKline PLC (GSK.L: Quote, Profile, Research), which had challenged the rules, and other companies with large patent portfolios.

The appeal will be filed with the U.S. Court of Appeals for the Federal Circuit, which hears patent appeals.

(Reporting by Diane Bartz)