LOS ANGELES — Two environmental groups are threatening to file a federal lawsuit against the Port of Long Beach unless it takes greater steps to clean up diesel pollution from ships, trucks and other vehicles.

The Natural Resources Defense Council and the Coalition for a Safe Environment yesterday sent port officials and the mayor of Long Beach a warning letter. The groups have given the port 90 days to come up with enforceable deadlines for its clean air initiative that they say is languishing.

Long Beach and neighboring Los Angeles harbor combined are the nation's largest port complex.

Concern over the effects of port pollution on surrounding communities led the two harbor commissions to approve a $2 billion clean air initiative in 2006.