* Hamilton on pole position
* Vettel sent to back of grid, will start from pit lane
* Ferrari's Alonso starts sixth (Adds stewards' decision)
By Alan Baldwin
ABU DHABI, Nov 3 (Reuters) - Red Bull's championship leader Sebastian Vettel will start Sunday's Abu Dhabi Grand prix from the pit lane as punishment for a fuel irregularity that could blow the Formula One title battle wide open.
Stewards stripped the 25-year-old of third place on the grid after post-qualifying checks on Saturday showed there was an insufficient quantity of fuel in the car for sampling purposes.
The ruling lifted Ferrari's Fernando Alonso, the Spaniard who is 13 points adrift of Vettel with three races remaining, to sixth place for the floodlit day-to-night race at the Yas Marina circuit where overtaking has been tricky in the past.
McLaren's Lewis Hamilton will start on pole position alongside Vettel's Australian team mate Mark Webber. Neither driver has any realistic hope of the title even if they remain mathematically in contention.
Vettel's grid position was questioned after his team and their Renault technicians ordered him to stop immediately on the track as he headed back to the pits after the chequered flag.
Red Bull were summoned to stewards to explain why the car had not been driven back to the pits under its own power, the same failing that sent Hamilton to the back of the grid at the Spanish Grand Prix after he had qualified fastest.
The decision was announced four hours and 40 minutes after qualifying had ended. The four stewards included Britain's former F1 driver Derek Warwick.
The stewards accepted telemetry evidence provided by the team that showed the car had stopped due to force majeure. However, the FIA technical delegate's report showed the fuel irregularity.
"The stewards determine that this is a breach of article 6.6.2 of the Formula One Technical Regulations and the competitor is accordingly excluded from the results of the qualifying session," the FIA statement said.
"The competitor is however allowed to start the race from the back of the grid."
Red Bull team principal Christian Horner said they had chosen instead to start from the pit lane so they could work on the car.
Horner said Vettel, who would have been chasing his fifth win in a row after leading every lap of the last three races, had taken the news calmly. The driver also did his best to sound upbeat in a team statement.
"One of the best ski jumpers of all times once said 'Every chance is an opportunity' and as far as we are concerned there are still plenty of chances tomorrow," he said.
Before Saturday, champions Red Bull had locked out the front row of the last three races and were looking likely to secure the constructors' title on Sunday for the third year in a row.
"It's the first time for a long time to be ahead of the Bulls and starting at the front," said Briton Hamilton, who was last on pole in Singapore last month but has always started on the front row in the Emirate.
"The car has felt beautiful all weekend," he added after his 25th career pole and sixth of the season.
Vettel, who had brake problems that sidelined him for most of final practice in the afternoon, had played down the qualifying problem earlier.
Vettel also brushed the guardrail in the first part of qualifying, sending out sparks, but appeared to escape without damage. He and Hamilton are the only drivers to have won at the harbourside track.
Alonso, whose car has shown better pace on Sundays than Saturdays in recent races, said he had done the best he could in the circumstances.
"We were not competitive today. I'm happy with my performance. We struck the maximum," the Spaniard said.
Venezuelan Pastor Maldonado will move up to third for Williams with Finland's Kimi Raikkonen, third in the championship with Lotus, lining up fourth. McLaren's Jenson Button will start fifth.
Michael Schumacher, who has not scored a point for four races and is retiring at the end of the season when Hamilton takes his seat, starts 13th for Mercedes while team mate Nico Rosberg moved up to seventh. (Reporting by Alan Baldwin, editing by Mark Meadows and Josh Reich)