By Eric M. Johnson and Mekhla Raina

(Reuters) - Rolls-Royce (RR.L) said on Thursday that turbine blades of its problematic Trent 1000 engines were wearing out faster than expected, grounding additional Boeing Co (BA.N) 787 widebody jets for early repairs.

Rolls-Royce said the issue may cause "additional short-term disruption" to customers in some cases, dealing a fresh blow to an engine program that has been dogged by design issues for the past two years.

The exact number of engines assigned for earlier-than-expected repairs related to the turbines blades on Rolls-Royce's package C series engines was not certain, but it could be as many as 30 or 40, a spokesman said. That is a small slice of the total Trent 1000 fleet.

"The guidance issued today is part of our ongoing management of the intermediate pressure turbine blade issue and applies only to the minority of engines which have not yet had replacement turbine blades fitted," the spokesman said.

The problematic turbine blades were already slated to be replaced, but were discovered to be deteriorating faster than expected, the spokesman said. The European Aviation Safety Agency (EASA) is expected to publish a formal requirement for repairs in the coming weeks, he said.

EASA did not immediately respond to a request for comment, nor did the U.S. Federal Aviation Administration.

Boeing spokesman Paul Bergman said safety remains the top priority as Rolls-Royce completes the replacement of intermediate pressure turbine blades on Trent 1000 engines.

"Rolls-Royce already has replaced the blades on a majority of engines," Bergman said. "Our team is fully engaged with Rolls-Royce, and deployed worldwide with customers to mitigate service disruption."

Rolls-Royce's civil aerospace president, Chris Cholerton, said over the summer that problems with the Trent 1000 engine had left some Boeing 787 Dreamliner planes grounded.

Separately, the compressor in the Trent 1000 package C engines is also not lasting as long as expected, requiring inspections and forcing airlines to ground aircraft while the checks take place. Some 380 of the affected engines are in service.

(Reporting by Mekhla Raina and Sathvik N in Bengaluru and Eric M. Johnson in Seattle; Editing by Leslie Adler)