Federal regulators are expanding the number of stocks covered by new "circuit breakers" that can pause volatile trading, a program in response to the panicked May 6 market plunge.

The Securities and Exchange Commission on Friday approved expansion of the six-month pilot program of circuit breakers for stocks in the Standard & Poor's 500 index. Now all stocks in the Russell 1000 index also will be covered.

The program, which began in mid-June, briefly halts trading of stocks that make big price swings. Trading of covered stocks that rise or fall 10 percent or more within a five-minute span is halted for five additional minutes.