SANTA ANA, CALIF. -- As highway shooting incidents signal mounting frustration over southern California traffic, officials here in nearly gridlocked Orange County are coming dangerously close to committing a cardinal California sin.

They want to build a toll road.

Paying for the privilege of using a highway goes against the deepest instincts of most westerners -- only Texas has toll roads of any consequence. But in a radical shift in conventional western politics, caused by a decade-long decline in public services, the California legislature appears ready to install the toll gates.

State Senate President David Roberti, a Los Angeles Democrat, called the idea "foreign to our way of life."

"Toll roads are a symbol of eastern decadence," said State Sen. Bill Lockyer (D) of Hayward. "It's a form of highway robbery."

State Sen. Gary K. Hart (D-Santa Barbara) said, "This is one of those legacies from Proposition 13, a fee for service, that I think is absolutely wrong for the state of California."

But when the Senate chamber in Sacramento had quieted, Sen. John Seymour (R-Anaheim), born in Pittsburgh not far from the Pennsylvania Turnpike, watched with satisfaction as his bill to allow as many as three toll roads in Orange County passed, 22 to 10.

He had persuaded his colleagues that the sprawling county, with 24 percent population growth during a decade of little road construction, could no longer cling to the image of having the best tax-financed freeway system in the world.

Mark Goodman, executive assistant to Orange County supervisor Thomas F. Riley, long ago gave up using the most direct freeway route, Interstate 5, for his morning commute from Laguna Niguel to the county seat here. He used to chance it in the summer, but the traffic no longer ebbs even then. Like many other county residents, he snakes his way around secondary highway and regular streets instead.

Supervisor Riley, a retired Marine general in his 13th year as a county supervisor, has little love of toll roads, despite remembering his excitement as a child when his family drove up from Harrisonburg, Va., to see the new Pennsylvania Turnpike. "With our freeways the way they are," he said, "we need to have that option if all else fails."

When some eastern states began in the 1930s to build a network of toll roads, California stuck to its gasoline tax to finance highways. At 9 cents a gallon, it brings in about $1.1 billion a year beyond federal highway funds. But several counties complain that it is not nearly enough.

Santa Clara, Alameda and Fresno counties have passed ballot measures raising the sales tax to pay for local roads. Orange County tried the same thing in 1984, but voters rejected the idea. The county received state authority to charge developers up to $1,200 for each new home in order to finance three crucial highway projects, but realized the fee would not be enough.

Each of the potential toll roads is designed to roughly parallel overloaded existing freeways. Gov. George Deukmejian (R), who could veto Seymour's bill if it wins assembly approval, said recently it is important to him that motorists "can make the choice, freely and voluntarily, . . . if they want to pay to ride on a particular stretch of highway."

One proposed toll route, now called the San Joaquin Hills transportation corridor, already has bulldozers clearing brush through coastal foothills between the San Diego and Pacific Coast highways. The projected 14-mile, $375 million road could be finished by 1995 if what some officials estimate would be a $1 toll is allowed.

California Department of Transportation (Caltrans) engineer Alex Dunnet said the department rates a highway as congested when traffic flow during a two- or three-hour period drops below 35 mph not counting times of accidents or lane closures. By that formula, Caltrans considered only three miles of Orange County freeway congested during morning and evening rush hours combined in 1970. Today that figure has grown to 148 congested miles.

Not only do longer hours on the freeway make voters think about changing supervisors and assembly members, but they contribute to violence, police here say. On July 18, a dispute over right-of-way in snail-pace traffic on the Newport-Costa Mesa Freeway led to a 28-year-old driver being critically wounded by another motorist with a gun. Similar incidents in Orange and Los Angeles counties have added to the general feeling, in the words of Jerry Kuhn, regional public service manager of the Automobile Club of Southern California, "that highway congestion is the No. 1 problem in the county."

There are 4,692 miles of toll roads in the United States, according to James F. McCarthy, policy evaluation chief of the Federal Highway Administration. A bit more than half are part of the federal interstate system and make up 5.7 percent of its length. A ban on federal financing of toll roads was lifted by Congress this year for seven "pilot projects" in Texas, Pennsylvania, Florida, South Carolina, Delaware, Colorado and Orange County.

The new law allows up to 35 percent of a toll road's construction money to come from the federal highway fund. Orange County officials expect to raise 45 percent to 50 percent of the cost from developer fees, leaving only 15 percent to 20 percent to be financed by tolls. Seymour's bill would forbid use of tolls to pay for highway maintenance. Once construction bonds were repaid, he said, the tolls would stop. But many critics, noting the problems of financing upkeep of existing roads, doubt that would happen.

California has 10 toll bridges and one private road, the scenic 17-mile drive near Monterey, that charges motorists a fee. The automobile club and some trucker associations want to keep it that way. "The problem with toll roads is that it costs so much to administer them," said Richard Barrett, highway design engineer with the auto club headquarters in Los Angeles. Setting up booths and collecting tolls would increase costs 14 percent, Kuhn estimated, while gasoline taxes paid by the same motorists could be raised with no added administrative cost.

Last week Seymour engaged in a heated argument with auto club lobbyist Bill Halloran before the state assembly transportation committee. Halloran charged that toll roads are elitist and could set a bad precedent for the state. Seymour shot back: "We're talking about a county that's in gridlock, . . . we're talking about a toll that is totally restricted to pay for construction only, and the automobile club has the audacity in representing its members . . . to oppose it? You're a disgrace, sir."

With some reluctance, after assuring themselves that Seymour's bill would not spread such unCalifornian activities to the rest of the state, the committee voted, 8 to 4, to send it to the assembly floor. The bill's prospects there are good, given Assembly Speaker Willie Brown's (D-San Francisco) willingness earlier this year to let a similar bill pass.

Brown noted the lack of Democrats among assembly members from conservative Orange County and called his help for the toll-road bill "a Democratic gift to you, sort of like the Marshall Plan to foreign nations."