NEW YORK – The major securities exchanges put aside some of their differences Monday and agreed to coordinate trading rules to prevent stock plunges like last week’s historic dive.

The Securities and Exchange Commission said the six exchanges agreed in principle during a meeting with regulators to a uniform system of “circuit breakers.” These restrictions would curb trading when the price of a stock or other security rises or falls to a specified level in the course of a trading day.

Four days after the plunge that sent the Dow Jones industrials down to a loss of nearly 1,000 points in less than 30 minutes, regulators were still saying publicly that they did not know the exact reason for the drop. But there was a growing belief that the varying trading rules on different exchanges contributed to the intensity of the selling and the size of the market’s slide.

People familiar with the situation said regulators believe the disruption was caused by the way different exchanges manage their trades and rapid price swings. A definitive answer could take weeks because regulators are going through information from across the market by hand, said the people, who spoke on condition of anonymity.