Adobe, Google and Yahoo are about to make it easier to build rich multimedia websites in the Flash file format (SWF) without sacrificing any “Google juice” (and, um, whatever the Yahoo equivalent is). Both search engines have been developing ways to fully index Flash content without requiring any extra effort from a website owner.

Previously, search engines indexed the “static” text and links on a site, falling far short of capturing all the content.

“It’s like reading the index of a book, rather than the book itself,” says Justin Everett-Church, a senior product manager for Flash.

Now, Google and Yahoo will read the whole darn book — namely, they’ll use web crawlers to play through all of a Flash website’s possible “states,” and make that content available through their search results. The previous “invisibility” of much Flash content to search engines has been a complaint from Flash developers and site owners, Everett-Church says.

Bill Hunt of advertising company Ogilvy tells me this move will particularly benefit “big brand” companies like jewelery maker Tiffany & Co., which has built a fancy shopping website in Flash. Until now, much of the site’s content, such as individual product pages, was invisible to search engines — they could only be seen by navigating the site itself, and wouldn’t turn up in Google searches. For example, it’s less-than-ideal that the top Google result when you search for “Tiffany gold ring” is overstockjeweler.com, rather than the Tiffany website.

This may be an even more significant announcement for businesses that have considered building Flash websites, but didn’t want to sacrifice their search rankings — now, if Google and Yahoo live up to their promises, no one will have to make that choice, removing one of Flash’s big drawbacks.

Everett-Church says that Google has already started tweaking its search results, while Yahoo’s development is a little further behind. Both companies are seriously pursuing this integration, he says, but I can’t help noticing that for now, this is yet another advantage that Google has over Yahoo. It’s hardly a huge setback, but it’s not like Yahoo has much ground left to lose.