United Continental trims service to Japan

* United Continental cuts back service to Japan

* Say reduction is temporary and in response to disasters

* Decline in demand for Japan trips is "measurable

CHICAGO, April 1 (Reuters) - United Continental Holdings Inc (UAL.N), parent of United Airlines, said on Friday it temporarily scaled back service to Japan because of sagging demand in the wake of last month's earthquake and tsunami.

"We're seeing a measurable decline in demand," spokeswoman Julie King said.

She said the world's largest airline -- formed last year from a merger of United Airlines and Continental Airlines -- would delay the start of the new San Francisco-to-Narita service and would cut some service on U.S.-to-Japan routes in May.

The carrier will eliminate 11 round-trip flights between Seattle and Narita, six round-trip flights between Washington D.C. and Narita; three round-trip flights between Los Angeles and Narita; and seven round-trip flights between Newark and Narita.

"It's a temporary reduction in response to the decline in demand we're seeing for travel," King said.

United's top U.S. rivals, Delta Air Lines Inc (DAL.N) and AMR Corp's AMR.N American Airlines, also are trimming service to Japan, which is still reeling from the natural disasters and radiation from a damaged nuclear plant.

United Continental shares were up 10 cents at $23.09 in midday trading on the New York Stock Exchange. (Reporting by Kyle Peterson; editing by Andre Grenon)