The Coast Guard interdicted more than 340 Cubans in the final two weeks of December, more than double the 140 who came in the first half of the month, before Mr. Obama’s Dec. 17 announcement that he would try to restore more normal diplomatic ties with Cuba. In the first seven days of January, another 144 came, keeping up the frenetic pace, according to Coast Guard records shared with Congress.

Mr. Obama’s announcement set off rumors that the U.S. would soon end its special immigration policies for Cubans, which sparked a scramble as migrants tried to beat what they believed to be a mid-January deadline for getting into the U.S., ahead of the immigration changes. The changes are merely rumors and no immediate action is pending, but they proved a powerful lure for hundreds trying the dangerous crossing.

“The Coast Guard protects our coastlines, and apprehensions of Cuban migrants could only be expected to increase in light of the Cuba decision,” said Rep. Duncan Hunter, California Republican and chairman of the House Transportation Committee’s subcommittee on the Coast Guard. “I hope the administration consulted with the Coast Guard through its decision-making, but nothing so far shows the administration did so to any great degree.”

Mr. Hunter wrote a letter Monday asking the Coast Guard to detail whether the White House consulted on its diplomatic plans.

Mr. Obama last month announced a prisoner swap with Cuba, sending home three Cubans serving time in U.S. prison for spying, and getting back an American government contractor, Alan Gross, and a U.S. spy in exchange.

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