UPDATE 1-Four major U.S. airlines seek new Japan service

* Treaty allows U.S. carriers to compete for service

* Delta, United, American, Continental seek routes

* U.S. DOT will determine service for daily flights (Recasts, adds other airlines)

WASHINGTON, Feb 16 (Reuters) - Delta Air Lines (DAL.N), the world's biggest airline, and three other U.S. carriers sought permission on Tuesday from regulators to boost its Asia service with flights to Tokyo's Haneda airport.

Applications to the U.S. Transportation Department to gain authority for up to four daily flights were also filed by United Airlines, a unit of UAL Corp UAUA.O; American Airlines, a unit of AMR Corp AMR.N; and Continental Airlines Inc CAL.N.

A treaty in December between the United States and Japan to liberalize trans-Pacific service opened Haneda, which has been closed to U.S. carriers for more than 30 years.

Mainly a domestic airport, Haneda has recently expanded to permit more flights. Its fourth runway is due to open in October.

Delta and United already fly to Japan through Narita airport. Delta wants to launch Haneda service from Detroit, Los Angeles, Seattle and Honolulu.

American wants to fly from New York's John F. Kennedy airport (JFK) and Los Angeles.

Continental and its subsidiary, Continental Micronesia, would fly from Newark, New Jersey, and Guam. United would fly from San Francisco.

U.S. regulators are expected to act swiftly on the requests.

(Reporting by John Crawley; Editing by Richard Chang)