SOCHI Russia (Reuters) - Formula One drivers have backed proposals to introduce a 'virtual safety car' or automatic speed limiter that would force the entire field to slow when yellow warning flags are waved.

The idea was raised by race director Charlie Whiting at the Russian Grand Prix on Saturday as one of the measures being considered following Jules Bianchi's horrific crash in Japan last weekend.

French driver Bianchi suffered severe brain injuries and remains 'critical but stable' after aquaplaning off a wet track while yellow warning flags were being waved and hitting a recovery tractor that was removing a crashed Sauber.

The 'virtual safety car' idea would mean drivers would respond to automatic GPS controls as if a safety car was deployed, but without it appearing on the track.

Some indoor go-kart circuits already use a system that cuts speeds at the push of a command from race control.

"We had a drivers' meeting with (FIA president) Jean Todt on Friday and one of the ideas that came out is in electric karts when a flag comes out and all the engines die or limiters are put on, which is quite good," said championship leader Lewis Hamilton.

"What's good is the FIA are reacting to it, they're trying to find the best solution," the Mercedes driver told reporters.

"The problem with flags is that you want to be safe, but you want to lose as little time as possible, so you're on a knife edge with it."

Ferrari's Fernando Alonso, a double world champion, said he had suggested the go-kart system in the drivers' briefing after visiting a kart track between the Singapore and Japanese rounds.

"If some kind of system can be done in F1, that it's the same for everybody, that everybody maintains the same gap... there is nothing to be done, just to go with the limit of the speed, then that is a good thing," he said.

Red Bull quadruple world champion Sebastian Vettel agreed the technology was there and the sport needed to do something as a result of Suzuka.

"What needs to be done is to make it as fair as possible. I'm sure we have the opportunity with the current systems and technology," he told reporters.

"It shouldn't be a big problem. It's just about finding the right compromise so everyone is happy."

McLaren racing director Eric Boullier told reporters separately that the sport could test a new system as early as the U.S. Grand Prix in Austin, Texas, in two weeks' time.

Whiting indicated on Friday, however, that the main aim was to ensure any changes were well thought through and to get them in place by the start of the 2015 season.

(Reporting by Alan Baldwin, editing by Toby Davis)