Similar experiments during the late 1960s and early 1970s, encouraged by federal financial incentives to combat a physician shortage, met with faculty opposition, according to a 1978 study by the Association of American Medical Colleges. But on tests, the study said, the three-year students performed as well as or better than four-year students.

The shorter programs were criticized for compromising basic science, reducing flexibility in the curriculum and pushing students to make career choices too early. Residency directors also felt uncomfortable accepting three-year graduates. About a quarter of the medical schools in the United States experimented with some type of three-year program in the 1970s, the study said, but they were quickly abandoned.

Two Canadian medical schools, at McMaster University in Hamilton, Ontario, and the University of Calgary in Alberta, have had their students in three-year programs for more than 40 years, officials at the two schools said.

The three-year programs at Texas Tech and Mercer are focused on producing doctors who want to go into family medicine, which administrators insist is not because family medicine is easier, but because they are responding to the need for more primary and preventive care.

That focus on only one category of doctors has disturbed some proponents of three-year schools. Dr. Bruce Wright, associate dean of undergraduate medical education at Calgary, said it could create a perception that three-year programs were “medical school lite,” turning out second-class physicians. The trend, he suggested, could ultimately lead to lower standards for family medicine graduates, who are already in a lower-paid, lower-prestige field.

N.Y.U. has decided to open its three-year program to students regardless of what branch of medicine they plan to go into, but Dr. Abramson said it would look for students interested in primary care fields like internal medicine, pediatrics and obstetrics. Students will have to declare their choice when they apply, because they will be guaranteed residencies in an N.Y.U.-affiliated hospital, as a way of lessening anxiety that other residency programs might be wary of their three-year degrees.

The adjustment would be easier for N.Y.U., he said, because it has already changed its curriculum to begin clinical studies in the first two years, rather than in the traditional third and fourth years, and it already accommodates some students who are earning both medical degrees and master’s degrees in public health within four years.