SACRAMENTO, CALIF., JULY 31 -- Motorists who clog California's freeways begin paying the state's biggest tax hike ever Wednesday morning, a voter-approved nickel-a-gallon levy on fuel that is aimed at reducing the highway gridlock.

The tax rises an additional cent Jan. 1, then one more penny each subsequent New Year's Day through 1994. That will provide the majority of funding for an $18 billion-plus, 10-year highway and mass-transit rail construction program that voters approved June 5 in the form of Proposition 111.

There was no organized opposition, and the scattered critics, for the most part, see the tax as unfortunate but necessary.

Some service station attendants in San Francisco, Los Angeles, San Bernardino and Sacramento said it was business as usual today while others said sales were up to 25 percent brisker as people stocked up before prices rose. A few stations said they ran out of gas.

The new levies will bring the state's gas taxes from 47th highest in the nation up to 37th after the first nickel hike, and to 12th when the full increase is in effect, said Penny Hill, a spokeswoman for the Road Information Program, a Washington-based nonprofit research organization.