George Clooney says gay marriage is "the final leg of the civil rights movement".

The actor is set to headline a benefit stage reading of 8, a play about the trial to overturn Proposition 8 and make same-sex marriage legal in California.

The Hollywood star explained that he thinks especially younger generations wouldn't have a problem with the legalisation of gay nuptials.

"I think the world is changing and it's becoming less and less of an issue and I think it shouldn't be long now," he told US website E! Online.

"I think younger people are looking at this like, 'Who cares?' I do believe it's generational, much like the civil rights movement," he continued. "Young people started taking to the streets and things changed. This really is the final leg of the civil rights movement."

But although he is well informed on today's issues, George explained why he doesn't think showbiz and politics mix particularly well.

The 50-year-old said that an actor's popularity and fame could do as much harm as good to a campaign.

"I've never campaignedeven when my father ran for Congress. I do fundraisers, but I don't think it looks particularly good to have actors out there on stage. You can still be polarizing. You can still actually bring as much harm as good and there's no point to it. Why take the chance?" he said.