SAN FRANCISCO (Reuters) - Chevron Corp will not have to face accusations from a prominent U.S. law firm that the oil major mounted a "smear campaign" related to long-running environmental battles in Ecuador, a U.S. judge has ruled.

Patton Boggs, a Washington D.C.-based firm representing Ecuadorean plaintiffs suing Chevron, had filed a separate lawsuit saying the company had tried to improperly interfere with its ability to represent the clients.

A judge in Ecuador's Amazon in February ruled against Chevron, demanding that the company pay $8.6 billion for contamination from petroleum drilling in the 1970s and 1980s by Texaco, which was later purchased by the giant U.S. oil company.

Chevron appealed that ruling. The company has also launched a series of separate legal proceedings in a bid to make any judgment unenforceable outside of Ecuador.

Patton Boggs had asked a U.S. judge to rule that its representation of the Ecuadoreans was proper. Tactics used by Chevron -- like threatening to disqualify Patton Boggs in various proceedings -- were tortious interference, the firm argued.

But U.S. District Judge Henry Kennedy Jr. granted Chevron's bid to dismiss the lawsuit on Tuesday.

"For this court to inform all other federal courts that Patton Boggs is qualified to represent the ... plaintiffs before those courts would be incredibly intrusive," wrote Kennedy, who is based in Washington.

A representative for the plaintiffs declined to comment. The lead Patton Boggs attorney on the case did not immediately respond to a message.

Theodore Boutrous, a lawyer for Chevron, said the lawsuit was "fundamentally flawed." Patton Boggs had sought to add Boutrous' law firm, Gibson Dunn & Crutcher, as a defendant, but Kennedy rejected that request.

"We are pleased that the district court so swiftly dismissed this frivolous and misguided lawsuit," Boutrous said.

The case in U.S. District Court, District of Columbia is Patton Boggs LLP v. Chevron Corporation, 10-1975.

(Reporting by Dan Levine, editing by Matthew Lewis)

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