America's war on terrorism appears to be helping the war on drugs, at least initially, as wary smugglers from Mexico avoid the risk of shipping their drugs across the border.

Under tight security with many more vehicle searches, the amount of drugs seized fell 80 percent along the 1,962-mile U.S.-Mexico border in the two weeks after the terrorist attacks, compared with the same period a year ago.

"The drug dealers, they're not stupid. They realize it would be risky to ship their stuff right now," said Kevin Bell, a spokesman for the U.S. Customs Service in Washington.

No one is suggesting drugs have become scarce in the United States. But authorities have long known that smugglers post spotters near border points to gauge security. Authorities expect the flow to surge again when the traffickers spot an opportunity, said Dean Boyd, a Customs official who analyzed seizure records along the border.

"The traffickers in Mexico don't want to sit on their product too long," Boyd said. "They've got to get it to market and pay their people."

Marijuana smugglers may not be able to wait much longer. The end of September marks their harvest season in Mexico and the dealers will be eager to move old supplies out of storage to make room for the fresh crop, said Jim Molesa, a Drug Enforcement Administration official in Phoenix.

"It's getting moldy," Molesa said of the old crop. "They're desperately going to want to get rid of it."

But the temporary drop after the attacks was significant, officials said.

Inspectors at California's border crossings, seized 4,179 pounds of marijuana, cocaine and other drugs Sept. 11-23. That was an 86 percent decline from the same 13-day period last year.

The story was the same to a lesser degree at other crossings: a 73 percent drop in the border sector that covers Arizona, New Mexico and West Texas and a 53 percent decline for South Texas.

The Immigration and Naturalization Service reported fewer illegal immigrants trying to gain entry as well. A typical weekend at the San Ysidro Port of Entry in San Diego, the world's busiest border crossing, would result in 500 people turned back or detained. Last weekend, it was 168.

The Rev. Luis Kendzierski, a Catholic priest who runs a shelter in Tijuana, Mexico, where men can stay up to two weeks while waiting to enter the United States, said would-be immigrants are waiting longer before risking the crossing.

"What I'm hearing is that nobody is making it through the checkpoints," Kendzierski said.

Within hours of the Sept. 11 attacks, Customs and INS inspectors were stopping and searching every vehicle and pedestrian that entered the United States from Mexico. Normally, agents question everyone but only conduct searches when they are suspicious.

They also added a metal detector at the pedestrian crossing in San Diego and authorized more overtime to increase the number of roving inspectors to move through the lines of people and cars with dogs trained to sniff out drugs.

These measures are in addition to an array of high-tech tools employed throughout the border, including X-ray-like devices that scan long-haul truck loads, digital license-plate readers and scopes designed to find contraband inside gas tanks.

Drug smugglers can avoid the ports of entry altogether and try to get their goods into the United States by alternate routes — by boat or overland through the desert wilderness between the border crossings.

But these methods also present challenges. The Coast Guard has been searching all foreign vessels entering certain U.S. ports, including San Diego, and Customs surveillance planes have been patrolling the Southwest border.

If the heavy security remains in force, officials believe the smugglers will begin taking risks. "Eventually they are going to try to get it across somehow," Boyd said.