WASHINGTON — The Trump administration took a key step Wednesday toward relaxing federal rules that govern the length of time that truck drivers can spend behind the wheel, a move long sought by the trucking industry but opposed by safety advocates who warn it could lead to more highway crashes.

The Federal Motor Carrier Safety Administration, an agency of the Transportation Department, issued proposed changes to the "hours of service" rules, which dictate breaks that truckers are required to take, and their time on and off duty.

"It puts a little more power back in the hands of the drivers and motor carriers," said Raymond Martinez, head of the federal safety agency. Martinez said the agency listened to drivers and their calls for safer and more flexible rules.

But highway safety groups have warned that putting the revisions into place would dangerously weaken the regulations.

There were 4,657 large trucks involved in fatal crashes in 2017, a 10% increase from the year before, according to a May report issued by the agency. Sixty of the truckers in these accidents were identified as "asleep or fatigued," although the National Transportation Safety Board has said this type of driver impairment is likely underreported on police crash forms.

Trade groups that represented truck drivers and motor carriers have pushed for years for less rigid hours of service rules, arguing that the regulations were too rigid and out of step with the daily realities confronting most truck drivers.

The existing regulations limit long-haul truckers to 11 hours of driving time within a 14-hour on-duty window. Drivers must have had 10 consecutive hours off duty before the on-duty clock starts anew. A driver who is going to be driving for more than eight hours must take a 30-minute off-duty break before hitting the eight-hour mark.

Under the proposed revisions, truckers could take a break while they are on duty but not driving. Drivers have complained that long waits for cargo to be loaded or unloaded keep them idle yet they are still required to take an off-duty break, even if they do not need to rest or cannot find suitable parking for a big rig.