WASHINGTON — Safety investigators told federal regulators three years ago it was dangerous for bus drivers to talk on cell phones while driving and recommended a ban.

The National Transportation Safety Board put that recommendation on its list of most important safety measures. Industry and safety groups had no objections.

Yet the regulatory agency that would write new rules on cell phone use by commercial drivers, the Federal Motor Carrier Safety Administration, has done little more than study the issue.

Now, after several high-profile accidents that focused public attention on using cell phones on the road, the Obama administration decided to act on the recommendation, which was left hanging by the Bush administration.

Transportation Secretary Ray LaHood will convene a two-day summit next week on distracted driving and plans to announce actions to address cell phone use by bus and truck drivers, said spokeswoman Jill Zuckman.

The NTSB's recommendation was prompted by a 2004 accident in which the driver of a motor coach carrying students on a trip to Washington became so engrossed in a cell phone conversation he failed to notice signs that said the height of an upcoming bridge was nearly 2 feet less than the height of the bus. The bus slammed into the underside of the bridge, shearing off the roof and injuring 11 passengers.

The safety board recommended the motor carrier administration prohibit commercial bus drivers from talking on cell phones except in emergencies and that it encourage states to do the same for school bus drivers.

The agency responded it would conduct studies to learn whether a new rule was needed and whether cell phone use by all commercial drivers should be prohibited.