O.C. Ready to Speed Up to 65 MPH on Sunday : Transportation: Santa Ana and San Diego freeways are among major Southland routes to be changed. Some L.A. County stretches will remain at 55 mph. Truck limit is unchanged.

Starting Sunday, the maximum speed limit on about 2,800 miles of freeway in California--including the Santa Ana and San Diego freeways in Orange County--will be increased to 65 mph from 55 mph, it was learned Monday. Another 1,400 miles are candidates for 70 mph, beginning in January.

All the major freeways in Orange, Los Angeles, Ventura and Riverside counties will increase to 65 mph, except for some of the busiest freeways through downtown Los Angeles and parts of the South Bay, Pasadena and San Fernando Valley.

Officials of the state Department of Transportation and the California Highway Patrol, who for several weeks have been selecting which routes will be boosted to 65 mph, are scheduled to announce their choices today.

Sources said road crews will start changing the 55-mph speed limit signs to 65 mph Sunday. The new posted limits will take effect immediately. The California speed limit for trucks will remain at 55.

In the Southland, the San Diego Freeway will be 65 mph, except from the Santa Monica Freeway south to the Orange County line, including the area around Los Angeles International Airport and the South Bay curve.

The Ventura freeway will increase to 65 mph throughout Ventura County and south until it reaches Topanga Canyon Boulevard in the Valley, where it will remain at 55 mph until it joins the Hollywood Freeway. The Hollywood Freeway will remain at 55 mph, as will the Pasadena Freeway and the Artesia Freeway in Los Angeles County.

The Santa Ana Freeway, between downtown Los Angeles and Orange County, will remain at 55 mph, pending further studies. The rest of freeway will increase to 65 mph, including the stretch through Orange County.

All the freeways in San Diego County also will jump to 65 mph, with the exception of California 163 in downtown San Diego, a section of Interstate 15 in North Park and California 78 east of Interstate 15.

Under legislation signed into law last month by President Clinton, the 55-mph national speed limit--imposed by President Richard Nixon in 1974 during the energy crisis--was repealed, and states became free to set their own limits.

In California, the process will occur in several phases, starting Sunday when the limit will be boosted to 65 mph on stretches of freeway where engineering and traffic safety studies have shown the higher levels are appropriate.

As a result of new legislation by state Sen. Quentin Kopp (I-San Francisco), other stretches of freeway, mostly in lightly populated rural areas, will be boosted to 70 mph starting next month, if justified by the studies. These are now posted at 65 mph.

Advocates of higher limits have argued that the 55-mph limit has been ignored by most California motorists. They assert that increasing the limit merely reflects the reality out on the road.

Traffic safety advocates, however, have warned that higher limits are certain to cause more highway deaths and injuries. They said traffic deaths fell dramatically after the 55-mph limit was set.

Officials also are examining various other routes throughout the state where the limit is 55 mph to determine if those limits should also be increased. The studies must be completed by March 31.

Likewise, local officials will study whether speed limits on roads in their jurisdictions can be raised to 65 mph.