UPDATE 1-U.S. patent office shortfall worsens -- official

* Patent office revenue dropping as economy worsens

* Officials working to avoid laying off examiners

(Adds facts and figures to give context)

By Diane Bartz

WASHINGTON, June 23 (Reuters) - The U.S. Patent and Trademark Office is facing a growing shortfall that has forced it to ask Congress for rule changes to help it weather economic hard times, a Commerce Department official told Reuters on Tuesday.

The patent office, which supports itself by collecting fees to grant and maintain patents, has seen its collections drop from $6.9 million a day in January and February of this year to $6.2 million per day in April and May, said Jay Reich, deputy chief of staff of the Commerce Department.

Last week, collections totaled just $5.9 million a day, Reich told Reuters.

Even before the financial crisis prompted companies to pare their patent portfolios, which reduced the patent office's revenue, the department was criticized for its large and growing backlog, which Reich estimated at 770,000 applications.

The 6,285 patent examiners approve or reject about 450,000 applications each year, according to patent office figures.