An alliance of liberal groups including the Christian Alliance for Progress, the Campaign to Defend the Constitution, and Talk2Action, have urged the giant retailer Wal-Mart, among others, to stop stocking the game, which was released last month.

"It's about religious warfare. The way to win is to convert or kill. You have both the Inquisition and the Crusades," says Frederick Clarkson of Talk2Action.

"Anybody who is not a follower of Jesus is the enemy," he claims.

'Dehumanising the enemy'

Mr Clarkson is particularly concerned that the $39.95 (£20) game - which is rated for teenagers due to violence - is being marketed through churches.

"Pastors and youth leaders recommend the game to their parishioners," he says, giving its message the stamp of authority.

And that message is the "dehumanisation of the feared other - Catholics, Jews, Muslims, the wrong kind of Protestants, people deemed to be sinners", he says.

That dehumanisation, he warns, is a first step towards genocide.

Jeffrey S Frichner, a co-founder of Left Behind Games, utterly rejects that characterisation of his game.

None of the missions in the game has a "convert-or-die" objective, he insists.

"It's the anti-Christ that desires you to convert or die, and you are defending yourself against that on the good side," he says.

"You will absolutely lose each level and never win the game if you choose physical warfare as a means."

'Evangelising - respectfully'

The word "convert" does not even appear in the game, he adds - and neither does the word "Christian".

"The game itself is just a great game. People of other faiths could play it and not know it's Christian," he says.

He freely admits the game aims to evangelise.

"But it is doing it in a way which is very respectful, not Bible-thumping."

When players successfully complete a level of the real-time strategy game, "you get a vignette that has some kind of Biblical truth and a find-out-more button", he says.

That leads players to a website where they can discuss issues, say a prayer and "become a believer", Mr Frichner says.

He thinks that will appeal to young people.

"People are drawn to things that provide answers. My personal position is that the Bible provides all those answers."

'Summer blockbuster'

Left Behind: Eternal Forces is not the first Christian video game, but it is the most ambitious to date, experts say.

"This is the first Christian developer that tried to produce a triple-A title, the summer blockbuster of video games," says Brian Crecente, editor of the games blog Kotaku and a video games writer for the Rocky Mountain News newspaper.

He is intrigued by the moral complexity of the game, which he saw played late in development, before its release.

"Your characters can do physical combat, but when they do, they lose morale and have a greater chance of becoming evil.

"In some sense, that can represent what happens. In the real world, you can't get involved in a gunfight and walk away and forget it."

He is critical of the game on other grounds, though, saying that in trying to deliver entertainment as well as a message, the developers have fallen short on both.

"It's a muddled message and a kind-of entertaining game," he says.

Kill the president

It is not the only violent video game with a message raising concern this holiday season.

The Global Islamic Media Front has released a game called Quest for Bush, in which players aim to kill the US president.

Adam Raisman, an analyst at the Search for International Terrorist Entities (Site) Institute who has played the game, calls the free download "propaganda", but stops short of labelling it recruitment.

"We can't say this is preparation for jihad, but it puts out the idea that you can walk around with a gun and shoot American soldiers," he says.

"It is putting the thought in your head that Bush, Blair and Rumsfeld are the guys you're going after."

Mr Crecente, the games writer, has not seen Quest for Bush (also known as Night of Bush Hunting, the literal translation of its Arabic title).

But he says both it and Left Behind: Eternal Forces are part of an effort in the gaming world to deal with important issues.

"Whenever games take on something important, they are accused of trivialising the subject," he says.

"This shows that video games have gotten past the birthing pains. They are no longer just about amusing people, but about trying to send a message."

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