They gather in groups in the brush alongside Interstate 5 - men, women and children from Mexico, waiting for a chance to dash across the busy freeway to a new life of opportunity.

Sometimes they don't make it.The interstate, which starts near the Mexican border and extends northward through Los Angeles, has become a ribbon of death for illegal aliens. Since 1987, 127 of them have been killed and 96 injured as they tried to outrun Southern California motorists while evading border agents.

"Most of these people trying to cross have no conception of high-speed traffic and don't know what freeways are," said California Highway Patrol spokesman Jerry Bohrer. "They don't have them where they came from.

"They see one car coming at 45 mph and think they can cross, but then the next car is doing 75 and they try to beat it and they get hit," he said.

Migrant advocates are alerting Mexican border communities by distributing small, yellow cards that show a man being struck by a car. "For the love of God, do not cross the highways," it reads.

Signs have been posted along Interstate 5 and other border-area freeways warning motorists to watch out for pedestrians.

State and federal officials believe the intense media effort to warn of the pedestrian dangers has helped. More than 90 days passed before two women were killed on Christmas Eve near the U.S. Border Patrol checkpoint at San Clemente.

Both sides want to do more, but they disagree on what further steps to take.

Migrant advocates are pressing for lower speed limits in areas where aliens cross. Bohrer said the highway patrol opposes the idea because sudden braking on the busy freeway would increase the risk of accidents. Instead, authorities plan to build a 5-mile-long, 8-foot-high barrier fence in the highway median near the checkpoint.

The fence, slated for completion in 1993 at a cost of $10 million, has drawn the ire of such migrant advocacy groups as the San Diego-based American Friends Service.

"The fence could conceivably trap them on the median, and they would have to run back across the freeway," said its director, Roberto Martinez.

The fence "could also become a Border Patrol enforcement tool because it would be easier to round up the undocumented people in the median," he said.

But Ben Davidian, regional commissioner of the Immigration and Naturalization Service, said the fence would prove a deterrent and denied the Border Patrol would use it to make its job easier.

"It is designed solely to save lives," he said. "We're not going to chase people along the median strip."

Pedestrian deaths have occurred mostly in two areas along Interstate 5.

One location is just north of the border, where aliens cross into the United States through remote areas and make their way east toward the freeway. There they hook up with smugglers who drive them north.

The other deadly spot is about 75 miles north of the border near the San Clemente checkpoint.

Kenneth Newmark of San Diego was driving southbound on Interstate 5 near the checkpoint last July when he hit and killed two people trying to cross the highway.

"They just came out of nowhere," he said. "They raced across the lanes. "I didn't even have time to hit my brakes."

Smugglers drop off the aliens on the median south of the checkpoint. The aliens have to run across four lanes of southbound traffic to get to San Onofre State Beach.

From there, they head north, avoiding the checkpoint and agents working the beach area. Beyond the checkpoint, they head east back toward the freeway and race back across all eight lanes to rejoin their northbound rides.