RIVERSIDE — The California Department of Transportation has recommended that $8.8 million be earmarked for a proposed commuter train from Riverside to Orange County that could relieve severe Riverside Freeway congestion.

Transportation officials said the state money would enable such a line to operate by 1993--about two years sooner than anticipated--and provide relief while car-pool and toll lanes are built on the highway. Construction on those additions, expected to begin later this year, will worsen congestion on the freeway.

The commuter train is the largest project recommended for a share of $65 million in gasoline sales taxes, said Robert Remen, executive director of the California Transportation Commission, which will decide next month whether to approve the Caltrans recommendations.

The money would be used to buy two trains that would make two round trips a day between Riverside and Orange County. A third train would be bought as a backup.

Riverside County officials said they could match the state allocation with about $8 million from the county's own sales taxes.

Even if that happens, the prospects for starting the service will hinge upon talks with the Santa Fe Railway Co., which uses the existing track as a main east-west artery into Los Angeles.

"All of this assumes we can get Santa Fe to agree to it," said Jack Reagan, executive director of the Riverside County Transportation Commission. "In a way, I think we are going to be at the mercy of Santa Fe in fitting them in to their freight lines. . . . They're supportive, but there's all kinds of provisions."

Dana W. Reed, chairman of the Orange County Transportation Commission, greeted the news of the Caltrans recommendation with enthusiasm, but he cautioned that the rail proposal still depends upon Santa Fe's cooperation.

"It affects us, because it will take cars off" the Riverside Freeway, Reed said. "I want to be enthusiastic and I want to help . . . but Santa Fe is a major concern."

If the rail link is approved, Santa Fe is expected to ask for capital improvements--such as alternate main-line tracks, switches and siding--because of the heavy load on the Santa Ana Canyon corridor.

Already, 27 freight trains and two passenger trains run along a single main line through the canyon each day, said Bob Harper, assistant manager for Santa Fe's regional office in San Bernardino.