The Rio Grande Valley sector is the busiest in the country for apprehensions of unauthorized immigrants, and the agent, Manuel Padilla Jr., said he called the meeting to prepare for the possibility of the first caravan’s arrival there. Mr. Padilla told those at the meeting that the caravan could arrive at the South Texas border, but it could also show up in towns as far away as California. Of particular concern to local officials is the potential for long lines at international bridges, as those in the caravan seek to enter the United States and apply for asylum.

“As far as we’re concerned, we want to make sure we focus on the ports of entry, so that there’s enough help at the bridges so people can get through the port and apply for asylum,” said Sister Norma Pimentel, who attended the meeting as the leader of Catholic Charities of the Rio Grande Valley, which assists migrants after they have been processed at the border and released. She said there was a concern that such large groups could overwhelm facilities along the border.

The officials discussed how to provide health assistance to the migrants. And since the meeting, the officials have been exploring options to add temporary housing, including at churches, because existing temporary shelter space is inadequate.

Chief Victor Rodriguez of the McAllen Police Department, who was also at the meeting, said he was always on standby to assist other agencies. But he was unsure what mission needed to be carried out as the caravan continued to head for the United States and the troops prepared to deploy.

“You’ve heard the saying: ‘This is a moving target,’” Chief Rodriguez said. “This is not even a target yet, it’s just moving. It’s like Jell-O. There are so many moving parts to this, and until we know what mission we’re trying to carry out, it’s hard for us to even plan to give assistance.”

The chief said he did not believe military options would be called for if and when the migrant caravan arrived in Texas. “My opinion is, if you were that person on the caravan down there and all of a sudden you see pictures of the military on the border, you’re getting the message that you’re not wanted,” he said.