Cushman Darby & Cushman, a Washington firm that specializes in intellectual property law, yesterday agreed to merge with Pillsbury Madison & Sutro, a San Francisco-based practice with more than 500 lawyers.

Once the merger takes effect on Aug. 1, the combined firms will have revenue of more than $227 million and will be staffed by nearly 600 lawyers, making it the nation's 10th-largest law firm.

The merger underscores the increasing cachet of intellectual property law, an area that has become a rich vein of litigation in recent years as the number of patents for new technologies has boomed. After years of ignoring the topic, many firms are now scrambling to get into the field -- Pillsbury included.

"This is a very happy days for us," said Stephen Stublarec, a Pillsbury partner and spokesman. "We decided about two years ago that in order to be a truly full-service firm, we needed some depth and expertise in intellectual property, and this merger is going to give it to us."

Pillsbury has 22 lawyers in Washington, most of them in regulatory and litigation practices. One of its better-known partners is Jay Stephens, a U.S. attorney under President George Bush. In February, the firm concluded in a report that it had not found the evidence needed to sue Hillary Rodham Clinton's former Arkansas law firm for its work on behalf of the failed savings and loan owned by the Clintons' Whitewater business partner.

Stephens refused to sign the report, saying he had done minimal work on it.

Cushman Darby is a 104-year-old firm that has earned its reputation through patent and trademark prosecution, licensing and copyright protection and software and hardware computer law. In 1995, the firm handled 1,624 U.S. patents, the third-highest total among all such firms.

"Intellectual property rights will be as important in the 21st century as were real property rights in the 19th and 20th centuries," Cushman Chairman Raymond Sweigart said in a statement.

The partners have agreed to retain the name Pillsbury, Madison & Sutro. The intellectual property practice will be consolidated into Cushman's D.C. offices.