July 18 (Bloomberg) -- Tate Modern, London's riverside art museum, revised plans for the new wing that architects Herzog & de Meuron are building for it, and said the 2012 opening may be delayed because of tough fundraising conditions.

At a press briefing, Tate Director Nicholas Serota and architect Jacques Herzog said the new building, designed in 2006 as a jagged cast-glass pile, will now be a brick polygon growing out of, and resembling, the existing Tate. They denied that budget reasons were behind the change, and maintained the project's 215 million pound ($429 million) cost, at 2012 prices.

``It's not cheaper,'' said Herzog, wearing a pale-pink T- shirt under his gray summer suit, as he showed slides of the new design. ``It's really to make everything better: more efficient, more compact, more flexible, and more green.''

In July 2006, Serota and Herzog showed reporters the previous design: an 11-story, 70-meter-tall extension shaped like an irregular glass pyramid. Reporters were taken to see the three disused oil tanks in the bowels of Tate which once held fuel to power London and sent smoke spouting out of the chimney. That plan has now been torn up.

Olympics Hope

Serota said today that construction on the new plan is scheduled to start in a year's time for completion by the 2012 London Olympics. However, the opening could be postponed to 2013 or 2014, and if not enough money is raised, he said, ``we won't do the building. It's as simple as that.'' He described current conditions as ``probably the most challenging time to raise money in the last 25 years.''

Serota said that when the July 2006 design was looked at again in January of this year, ``we realized that Tate's brief had changed in a number of significant ways. We mutually agreed we should revisit the scheme.''

The three oil tanks, which were to be used as an auditorium and a performance space, become display areas, following artists' suggestions, forming the base of the new extension.

The new plans will also allow Tate Modern to be more environmentally friendly by using 40 percent less energy and generate 35 percent less carbon.

Expressed in 2006 prices, the project's cost is 165 million pounds. So far, Tate has received 50 million pounds from the government, 7 million pounds from the London Development Agency and 13 million pounds from private donors.

To contact the reporter on this story: Farah Nayeri in London at Farahn@bloomberg.net.

Last Updated: July 18, 2008 12:32 EDT