WASHINGTON — With little fanfare, the Obama administration has been pursuing an aggressive campaign to restore protections for workers that have been eroded by business activism, conservative governance and the evolution of the economy in recent decades. “These moves constitute the most impressive and, in my view, laudable attempt to update labor and employment law in many decades,” said Benjamin Sachs, a professor at Harvard Law School and a former assistant general counsel for the Service Employees International Union. Labor unions complained that he failed to throw his energy behind a measure that would have made it easier for workers to organize by requiring employers to recognize a union once a majority of workers had signed cards, rather than allowing employers to insist on a secret ballot election. Since he has not been able to advance legislation through the Republican-controlled Congress, Obama has failed to achieve a number of important goals, most notably raising the federal minimum wage. Liberals and union supporters, while applauding Obama’s record in the narrow realm of labor rights, complain that he has undercut workers with his efforts to promote global trade agreements and balanced budgets. “As long as the budget deal the administration negotiated continues to restrict domestic discretionary spending,” the Labor Department’s ability to enforce the laws guaranteeing workers a minimum wage and overtime pay “and fight misclassification will be severely limited,” Ross Eisenbrey, a researcher at the Economic Policy Institute who was one of the architects of the overtime regulation, said in an e-mail.