LOS ANGELES, JULY 27 -- A surge in street and highway shootings here since mid-June has exploded into a murderous epidemic, with five incidents last weekend that left three men dead and two others slightly injured.

"It's a war out there," said Dr. Ange Lobue, a UCLA and College Hospital of Cerritos psychiatrist specializing in stress management.

The California Highway Patrol and local police report 10 roadway shootings since June 18, with a total of four dead and two seriously injured. The pace of reported shootings has accelerated in the last week, with one Saturday, July 18, one Monday, one Friday, one Saturday and three Sunday. Medical and law enforcement authorities attribute the bloodshed to record traffic on southern California freeways, hot weather and Californians' love of their cars.

In the latest incident, Los Angeles police said two men, Manuel Brown Avila, 28, and Angel Aguirre Barrera, 36, were found dead about 6:45 p.m. Sunday near Avila's car at a stop sign in Sylmar, a community in northwestern Los Angeles. A witness said a motorist shot the two men after Avila failed to move his car past the stop sign, although police said they were also investigating a possible gang warfare motive for the crime.

Earlier Sunday, two men were slightly injured when a man driving a foreign sports car became enraged during an argument on the crowded Pacific Coast Highway in Santa Monica and fired several shots into a pick-up truck. Police said one passenger received powder burns and another received minor cuts from broken window glass. Another bullet pierced a safety helmet being held by a motorcyclist, but he was not injured, police said.

Police in Alhambra, northeast of downtown Los Angeles, said six shots were fired from a blue pick-up truck at another vehicle on the Long Beach Freeway about 4 a.m. Sunday, leaving three bullet holes but no injuries.

Authorities said they had not followed up the Alhambra report, despite the general similarity between the assailant's description and that of a man who allegedly killed 17-year-old Russell Pirrone Friday night in Pomona, 20 miles away. Pirrone was shot after pulling his Volkswagen in front of a blue pick-up whose occupants complained loudly that he had cut them off.

"People take on a whole different personality behind the wheel," said highway patrol Sgt. Mark Lunn. The hot weather and traffic did not improve drivers' personalities.

Lunn and Lobue noted that Californians often identify strongly with their automobiles. More than 1.5 million motorists in the state -- about 7 percent of the total -- have personalized license plates, a higher percentage than in any other state.

"A man's automobile is his castle," Lobue said. Such territoriality and the stress of congested highway driving -- on top of everyday worries such as being late for work or angry at a spouse -- can provoke violence, he said. Police and psychiatrists also say publicity given to the rash of shootings may encourage some emotionally disturbed drivers to add to the statistics.

"The scums now know that this is a crime they can get away with, without even leaving a tire mark behind," said Paul Barrera, a Pasadena real estate broker who serves as regional coordinator for the Guardian Angels. Two of the 10 incidents have resulted in arrests.

Police and psychiatrists have warned motorists not to respond aggressively to annoying behavior by other drivers. The Guardian Angels, a crime-fighting group with seven local chapters, said today it is sending patrols onto the freeways. The group encouraged motorists to display yellow ribbons as signs of cautious driving and report unusually aggressive drivers.

According to the highway patrol, the series of shootings began June 18 on a freeway near the desert community of Newhall when three bullets from a passing truck narrowly missed a motorcyclist.

Two days later, on the Santa Ana Freeway near Santa Fe Springs, Rick Lane Bynum, 24, was killed by a motorist with a .38-caliber pistol. Bynum's girlfriend, who was driving the car, said the motorist appeared upset that she had not pulled over to let him pass immediately after he signaled her with his headlights.

On July 18, Paul Gary Nussbaum, 28, was shot in the neck after a dispute on the crowded Newport-Costa Mesa Freeway. Albert Carroll Morgan, a 32-year-old roofer, was later arrested in connection with the shooting as he and his wife attempted to drive into a nearby fairgrounds. Nussbaum remains partially paralyzed and in serious condition.

The second highway shooting arrest occurred two days later, after a Northridge woman pursued and wrote down the license number of a car whose driver allegedly fired three times at her and a male passenger. Lewis L. Meeks, 32, an unemployed carpenter, has pleaded not guilty to charges of attempted murder.