Nurse practitioners would be allowed to treat patients and prescribe medications independently under a proposal by Gov. Dannel P. Malloy's administration, a potentially significant — and controversial — change in the medical landscape aimed at expanding access to primary care. The ability of nurse practitioners to work independently of doctors has long been an issue of contention between the two professions, and states vary widely in how they allow nurse practitioners to practice. But the federal health law commonly known as Obamacare puts the debate in a new context: The expansion of insurance coverage to thousands more people is expected to raise the demand for primary care, at a time when the state already faces a shortage of primary care doctors and an aging physician population.