It is an obscure art of Wall Street, a technique that gives a scattering of traders an edge over everyone else  and the Securities and Exchange Commission wants to stamp it out.

The S.E.C. on Thursday proposed banning what are known as flash orders, which use powerful computers to glimpse at investors’ orders. The practice is often associated with a controversial corner of finance called high-frequency trading, which has grown, largely hidden from view, into a potent force in the markets.

The proposed ban was announced on the same day that the S.E.C. put forward new rules for credit ratings agencies, which were widely criticized for their role in the financial crisis. Together, the moves telegraphed a tougher line from the commission after a series of prominent missteps, including its failure to spot the Ponzi scheme orchestrated by Bernard L. Madoff.

Critics say flash orders favor sophisticated, fast-moving traders at the expense of slower market participants. Using lightning-quick computers, high-frequency traders often issue and then cancel orders almost simultaneously and get an early peek at how others are trading.