When used properly in the early weeks of pregnancy, misoprostol, which causes uterine contractions and cervical dilation, induces a miscarriage about 85 percent of the time, according to Dr. Grossman. But many women receive incorrect advice on dosage and, especially later in pregnancy, the drug can cause serious bleeding or a partial abortion, he said.

The looming limits on legal abortion follow deep cuts in state support for family planning. Planned Parenthood clinics here in Hidalgo County do not perform abortions, but in 2010 provided subsidized contraception to 23,000 men and women at eight centers; as financing dried up, four of them have been closed. This year, the group will serve only 12,000 clients, and other organizations have not taken up the slack, said Patricio Gonzales, chief executive of the Hidalgo County chapter of Planned Parenthood.

If legal abortions become inaccessible in this part of the state, Mr. Gonzales said, “Planned Parenthood may have to step up” and try to raise $1.5 million or more to build a new surgery center that meets the requirements of the new law.

Lucy Felix, a community educator here with the National Latina Institute for Reproductive Health, said that many of the women she works with do not have legal residency and cannot drive north in Texas through Border Patrol checkpoints or even cross the southern border to buy the pill directly for fear that they may not be able to return to their families in Texas.

“The only option left for many women will be to go get those pills at a flea market,” Ms. Felix said. “Some of them will end up in the E.R.”

The two abortion clinics in the Rio Grande Valley say that the cost of meeting ambulatory surgical center standards would be prohibitive. They also doubt that they could find nearby hospitals that would grant admitting privileges to the abortion doctors, another element of the new law.

“They will close us down,” said Dr. Lester Minto, who owns the Reproductive Services clinic in Harlingen, which performs 1,500 to 2,000 abortions each year for a price of about $400.