Lost job hunters never even know when they’ve lost out on an interview because of “digital dirt.” That could include your chat-room tirade on an ex-roommate’s sex life or that photo of you and college buddies smoking something that’s not exactly tobacco – stuff a prospective employer finds by Googling your name that causes her to scratch you off the “to call in” list.

Such ignorance would have been bliss for Hamilton Linn who, back in 1997, the days before we Googled everything, was interviewing with an Internet Explorer manager at Microsoft headquarters. The interviewer called up on his screen Linn’s personal Web page, which revealed:

l Linn’s advice for people to use Netscape Navigator instead of Explorer.

l A photo illustration of Bill Gates morphing into the devil.

Granted, it was back during the “browser wars,” before Explorer emerged as king. And the photo was actually a link to the site of his Bill Gates-hating friend. But “suffice it to say, the rest of the interview didn’t go well,” says Linn, 27, of New Hyde Park, N.Y. “Needless to say, I didn’t get a job offer at Microsoft.”

Today, job hunters can count on being Googled. Three out of four recruiters do Internet research on candidates and one in four has dropped candidates based on what the searches found, according to 102 recruiters responding to a “digital dirt” survey conducted by ExecuNet, a Norwalk, Conn.-based networking organization for high earners.

Of course, you might say, your opinions, rants and mementos of playful moments have nothing to do with your job qualifications. But, ExecuNet chief executive David Opton says, like it or not, “how you present yourself to the world goes beyond 9 to 5.”

It shows “you don’t know how to manage your professional reputation,” says Charlie O’Donnell, an analyst with a New York-based venture capital firm. He also writes blogs on several subjects, including the use of blogs as career development tools, at Successblogging.com.

Nevertheless, “you don’t have to pretend you don’t have a life after work,” he says. Online photos of you and friends enjoying happy hour are fine as long as you’re not doing a hula on the bar, or worse.

And some of your beliefs and opinions may trump certain jobs. One of O’Donnell’s friends worked in public relations for a reproductive rights organization, and those press releases she wrote are high on the list of Google links to her name. But, says O’Donnell, her feeling is that she probably wouldn’t want to work for someone who would object.

Of course, experts tell us not to post anything online that we wouldn’t want a prospective boss to see. And if we all behaved impeccably, we would refrain from saying anything salty or sassy – and what a boring place the Web would then be.

“You don’t want to miss out on digital wave riding. The whole thing is fun, it’s historic, and you want to be a part of it,” Keshia Richmond says. “I would adopt a pseudonym.”

That would protect your privacy, as well as your livelihood, says Richmond, who was caught in two online transgressions – after she was hired: posting her resume to a job board, and setting up a Web site for an after-hours work endeavor. She talked her way out of the first, but not the second. She’s now her own boss at Richmond Technology Solutions Inc., a New York information technology consulting firm.

For those who should have used a pseudonym but didn’t, here are some thoughts on digital dirt damage control.

First, get rid of anything truly tacky that you control, and ask buddies to do the same. Do not, though, try to get other Web sites or blogs to remove your comments, especially if you’ve engaged in a fiery debate, says O’Donnell. Your request may well get posted, along with who knows what else.

Counterbalance the negative dumb stuff by posting more professional-sounding smart stuff on frequently visited, well-respected blogs or forums, ones that emerge high on the list of Internet search results. Those classier, image-enhancing comments should bump the others down further on the search results list, even to the second or third page.

You can use your own blog or Web site to put some of your rants and inflammatory comments posted elsewhere in perspective. OK, it’s called spinning it to your advantage, Linn says.

And, despite his missed opportunity at Microsoft – a “blessing in disguise,” he calls it – he went on to work for Goldman Sachs and now runs Wall St. Training, which helps new hires at investment banks get up to speed in financial analysis areas.

Even if you’re squeaky clean, an employer may still find dirt attached to your name. That’s because someone with the same name is out there ranting on Nazi-type sites or proposing odd activities with orangutans.

Which makes it useful to set up a Google alert, Richmond says, which will let you know by e-mail whenever your name – or one just like it – shows up on the Internet.

O’Donnell shares this advice: The best way to get interviews and jobs is through personal contacts – and that means being part of an active network of professionals, people who will vouch for you.

“If Google is the only place people go to find out about you,” he says, “then you’ve got a problem.”