The U.S. Securities and Exchange Commission is considering regulatory changes aimed at slowing stock trading during periods of cascading prices, even though the agency hasn�t yet concluded what caused this week�s market plunge, two people familiar with the matter said.

SEC officials are weighing whether uniform trading curbs should be imposed across markets for companies that have fallen a certain percentage, said the people, who declined to be identified because the discussions are preliminary. The agency is examining whether any rules should include a time element because a steep decline that occurs in minutes may be more detrimental to markets than a decline over several hours, one of the people said.

U.S. regulators and exchanges are trying to determine what happened after stocks fell May 6, temporarily erasing more than $1 trillion in market value, in a rout fueled by waves of computerized trading. The SEC and Commodity Futures Trading Commission said in a joint statement yesterday that declines for individual stocks were �inconsistent� with well-functioning markets and pledged to make �structural� changes if necessary.

SEC spokesman John Nester declined to comment on internal agency discussions. Lawmakers are pressing the SEC for answers.