EDINBURG, Texas – The Border Patrol in one of Texas' five sectors has seized about 50 tons of marijuana just 10 weeks into the fiscal year, a huge increase that the sector chief attributes to a change in immigration policy that has allowed agents to focus on drugs.

The spree of seizures in the Rio Grande Valley sector culminated this week with a three-day catch totaling more than 10 tons, including a 7,000-pound load in a tractor trailer heading through a highway immigration checkpoint.

The increase in seizures of 181 percent over the same time last year can be traced in part to so-called "other than Mexican" immigrants no longer being turned loose after capture with a notice to appear before a judge, which they often ignored, sector chief Lynne Underdown said Thursday. Unlike Mexicans, other illegal immigrants can't be immediately deported.

Word apparently has reached non-Mexican immigrants that they can be detained and eventually deported, and apprehension numbers are down 70 percent, Chief Underdown said. As a result, she said, agents can spend more time chasing drug traffickers.

"We have gained control in the area of aliens," she said.

There have been reports of a bumper crop of marijuana because of unseasonably heavy rains in Mexico, which could lead to increased flow of the drug across the border.

"The fact that we've gained this level of increased control in our area has enabled us to keep our agents out in the field as much as possible," Chief Underdown said.

She said the fact that traffickers would attempt to bring a load through a checkpoint signaled desperation as agents patrol other routes, including some revealed through new mapping technology.

"Our agents are out on the road, disrupting those organizations that used those back roads," she said.

Javier Rios, a Customs and Border Protection spokesman in Washington, said that marijuana seizures along the Southwest border were up 21 percent over last year and that cocaine seizures had increased 69 percent.

He said the Tucson sector led in marijuana seizures, followed by the Rio Grande Valley and El Paso.

"Expedited removal, detention capacity and improved removal has led to a decrease in the numbers of cross-border traffic," Mr. Rios said. "With less traffic, the agents are able to expand their enforcement effort."