Circuit overload taxes ingenuity of phone company line monitors.

The California Highway Patrol dispatches an entire army of officers to keep the Southland's jam-packed roadways flowing. But Pacific Bell has just six people keeping its local telephone "roadways" flowing.

Those six people spend each workday monitoring the more than 8,000 tiny lamps -- red, green, amber and white ones -- that indicate when, where and what is preventing Angelenos' phone calls from going through.

The lamps are on a 60-foot-long by 12-foot-high gray, concave switchboard at a secret location in Pasadena.

The building's specific address is not publicly revealed because "if someone wanted to disrupt the phone network, a disruption to that building could be critical," a Pac Bell spokesman said.

This is the switching "nerve center" of Pac Bell's "service area five," which extends from San Clemente to Ventura, from the ocean to the California-Nevada-Arizona borders.

Pac Bell has about 250 switching offices in service area five, and its six-member "network management" team in Pasadena is charged with keeping phone traffic moving smoothly among those switching offices.

The job can be challenging at peak call times, during which the gigantic gray switchboard can light up like a Christmas tree.

"The highest-volume day is Mother's Day," explains Tony Welch, one of Pac Bell's six L.A. network monitors. "Christmas is also pretty busy, and so is the first workday following a long holiday weekend."

But phone-traffic bottlenecks occur with regularity in certain areas of Los Angeles.

"We have a high-volume 520 network that goes to all the call-in radio and TV shows," Welch says. "We see overflow conditions on that network quite often."

An "overflow condition" exists whenever the volume of calls going into or out of a particular area's switching office exceeds the capacity of that office's transmission "trunks." When that condition exists, a red light flashes on Pac Bell's big gray board in Pasadena. And Welch and his co-workers spring into action.

The first re-routing option is to switch the overflow calls to one of four higher-class, or "mother," switching stations located in service area five.

The local "mother stations" are in downtown Los Angeles, Gardena, Sherman Oaks and Anaheim. The first re-route option involves switching overflow calls to the receiving, or terminating, end's mother station.

For example, if a caller in Burbank is trying to place a call to someone in downtown Los Angeles, but all the trunks between Burbank and downtown are operating at capacity, Welch or another network monitor will re-route that call through the "mother" station in downtown Los Angeles.

However, if the terminating end's mother station is also operating at capacity, the call will be re-routed through the originating end's mother station.

In our example, the mother station serving Burbank is in Sherman Oaks. So, if the downtown mother station is operating at capacity, Welch would re-route the Burbank-to-downtown call through the Sherman Oaks mother station.

If both the originating and terminating mother stations are operating at capacity, the call would be switched to a pre-recorded-message network, where the caller hears the "All circuits are currently busy" message.

Finally, in the event that pre-recorded-message network is operating at capacity, the caller will hear an "all-circuits-busy" signal. That all-circuits-busy signal is twice as fast as a "normal" busy signal, which indicates the party dialed is talking to someone else.

In other words, many alternate routes are tried before a caller is given the circuits-busy signal. But, just as with freeway gridlock, some phone roadblocks just have to be waited out.

In extreme cases, Pac Bell can switch calls through the mother stations of General Telephone, or any other phone company operating a system in the overloaded area.

Welch, who has been monitoring phone-traffic flows in Los Angeles for five years, said he now can ascertain the cause of a particular jam-up in many cases.

"I ask myself, 'Why are people all picking up their phones simultaneously and calling, say, Arcadia, or downtown Los Angeles?'" Welch said. "A high volume of activity to Arcadia usually means something is going on at the (Santa Anita) racetrack."

"Right after the Rodney King video was shown on the news," Welch continued, "calls started flooding into the LAPD and City Hall in downtown L.A. When we see a surge at 3:30 or 4 in the afternoon, it typically has something to do with a kids' show contest on TV."

Pay-per-view events on TV, especially high-profile boxing matches, also send Pac Bell's big gray switchboard into a flashing fit of color.

"The night of that last big fight in Las Vegas. I worked until one in the morning," Welch remembers.

Callers who want to minimize the frustration of hearing the all-circuits-busy signal might want to consider dialing during off-peak hours.

Peak weekday hours are between 10 and 11 a.m., Welch explained. At that time, most people on the West Coast are at work, and most people on the East Coast are back from lunch. The evening peak hour is between 8 and 9 p.m., when most West Coast people have finished dinner and most East Coast people are not yet asleep, Welch adds.

Callers continually getting an all-circuits-busy signal are advised to contact their Pac Bell representative. It might be an indication that the trunk capacity of the area's switching office needs to be expanded.

Sometimes Welch and his co-workers have to reduce a network's capacity. A prime example of this is following a major earthquake or fire. In these situations, incoming calls, most of which are from concerned relatives and friends, have to be "choked" at a volume far below full capacity so that more capacity can be freed up for out-going calls.