The Obama administration is planning to use the government’s enormous buying power to prod private companies to improve wages and benefits for millions of workers, according to White House officials and several interest groups briefed on the plan.

By altering how it awards $500 billion in contracts each year, the government would disqualify more companies with labor, environmental or other violations and give an edge to companies that offer better levels of pay, health coverage, pensions and other benefits, the officials said.

Because nearly one in four workers is employed by companies that have contracts with the federal government, administration officials see the plan as a way to shape social policy and lift more families into the middle class. It would affect contracts like those awarded to make Army uniforms, clean federal buildings and mow lawns at military bases.

Although the details are still being worked out, the outline of the plan is drawing fierce opposition from business groups and Republican lawmakers. They see it as a gift to organized labor and say it would drive up costs for the government in the face of a $1.3 trillion budget deficit.