The next holy grail of advertising on the World Wide Web is an elusive concept called one-to- one marketing.

The idea is that Web sites eventually will be able to identify their visitors and serve up content and advertising to fit their palates.

``The more you can describe the audience, the more you can charge (for the ad),'' said Ali Partovi, chief strategist at the Internet Link Exchange, a San Mateo startup that places ads on the Web.

But so far, Web advertisers have found it hard to compile precise data about Web viewers.

Now two Bay Area companies have released software packages that aim to provide the tools for one-to-one marketing.

Accrue Inc., a Mountain View company, announced a $15,000 software package yesterday that allows Web sites to track users by where they came from, how long they spent on a page and how long it took them to download a page.

Andromedia Inc. in San Francisco offers a software package -- which ranges in price from $1,800 to $50,000 -- for Web sites to track the same information.

Both companies strive to offer Web sites a live picture of what is happening on their pages.

Theoretically, that means Web sites will be able to tailor pages to visitors.

``Advertisers won't have to say, `Give me 25 men between the ages of 25 and 30.' They'll just say, `Give me people who own tennis rackets.' '' said Tom DuBois, vice president of business development at Accrue.

Accrue's software was originally dreamed up at Organic Online, a Web development company in San Francisco. Accrue has raised more than $2.5 million in venture capital and is partially owned by Organic Online and CKS Group, an interactive marketing firm in Cupertino.

Andromedia shares the same vision, and is financed by Japanese publishing giant Softbank and venture capital firms Draper Richards and Platinum Ventures.

``When TV was invented, the first programs were just videotaped radio,'' said Kent Godfrey, CEO of Andromedia.

``I think the Internet is in the same boat,'' he said. ``Most of the content is just repackaged broadcast content. It's not really taking advantage of the online capabilities.'' But in practice, most Web sites' concerns are more down-to-earth -- they simply use the tracking tools to find out what's going on at their site. ``Mostly we want advertisers to know who has clicked on their ad,'' said Michael Lynch, Webmaster at New Media magazine in San Mateo, which uses Andromedia's software.

And Webmaster Crain McWhitish used Accrue's software to discover that some visitors to www.bigbook.com were waiting three seconds to download a page, while others got it in less than one second.

``We're still trying to narrow it down to what that specific problem is,'' he said. ``But we had no idea there was even that gap before.''

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