WASHINGTON  The Obama administration’s sweeping new proposal to restrict executive pay is likely to be a humbling exercise for seven of the nation’s largest companies, which have received billions of dollars in federal assistance to survive the economic crisis.

But for most other companies, the plan is expected to have only a marginal effect on pay practices for now.

The Treasury Department on Wednesday appointed a well-known Washington lawyer, Kenneth R. Feinberg, to oversee the compensation of employees at the seven companies  the American International Group, Citigroup, Bank of America, General Motors, Chrysler and the financing arms of the two automakers.

He will have broad discretion to set the salaries and bonuses for their five most senior executives and their 20 most highly paid employees.