The Obama administration said Tuesday that it had shelved plans for a survey in which "mystery shoppers" posing as patients would call doctors' offices to see how difficult it was to get appointments. "We have determined that now is not the time to move forward with this research project," the Department of Health and Human Services said late Tuesday. The decision, after criticism from doctors and politicians, represents an abrupt turnabout. On Sunday night, officials at the health department and the White House staunchly defended the survey as a way to measure access to primary care, and insisted that it posed no threat to privacy. Health policy experts have long expressed concern about a shortage of primary care doctors, including family physicians and internists. The shortage, they say, could become more serious if, as President Obama hopes, more than 30 million people gain insurance coverage under the health care law passed last year.