MySpace , the wildly popular but so far unprofitable News Corp. ( NWS) Web site, will double its sales force this year.

The move will bring the sales force of MySpace, which News Corp. bought last year for $588 million, to about 30, says Michael Barrett, the chief revenue officer for News Corp.'s Fox Interactive Media. The new hires have been "specifically budgeted," he says in an interview.

Bringing more advertising dollars into MySpace without alienating its more than 50 million unique visitors is going to be tricky, but it's a gamble that New York-based News Corp. needs to make. The site is the focal point of Rupert Murdoch's Web strategy -- a strategy that has been a hit with investors this year.

Last week, News Corp. unveiled the first leg of its effort to make MySpace pay off, in a $900 million ad linkup with Google ( GOOG).

Now, advertisers say the company is stepping up its efforts to convince big clients using MySpace's free Web pages, known as profiles, to become paying customers as well.

"MySpace has started to reach out to companies that are setting up commercial pages on the site, encouraging them to reach some kind of financial agreement and forgo the free ride," says Jeff Lanctot of aQuantive's ( AQNT) Avenue A|Razorfish online advertising agency. "While this could include paying to have the page up, I think buying an ad package to support the commercial page is also a reasonable solution."

MySpace denies that it has changed its sales practices dramatically. What advertisers may be noticing are the site's efforts to better articulate to clients the value they get from working with the site, says Fox's Barrett.

"I think we've gotten more clear with our marketing partners about different types of functionality on their profiles and the costs associated with that functionality," he says. "We haven't always articulated that value proposition clearly."

MySpace's rules forbid advertisers from using profiles for commercial purposes that haven't been approved or endorsed by the site. Users also are forbidden to use MySpace to send spam.

MySpace's so-called enhanced profiles -- or ads -- can cost between $500,000 and $700,000 per campaign, Fox's Barrett says. He says some companies, which he wouldn't name, have spent seven figures on their MySpace pages.

News Corp. will get some help promoting MySpace from the deal it signed last week with Google. The owner of 20th Century Fox will get $900 million over four years. Google also has a right of first refusal on display advertising sold through third parties on Fox Interactive Media's network.

There's plenty at stake. Though MySpace's ad sales are expected to be a modest $180 million this year, they will rise to more than $1 billion by 2010, according to an estimate by the research firm eMarketer. News Corp.'s revenue this year is expected to top $27 billion, according to analysts surveyed by Thomson Financial.

"I'd rather them not try to nickel and dime the site," says Darren Chervitz of Jacob Asset Management, which owns News Corp. shares. "If there is a way for MySpace to generate additional revenue without alienating its user base, I as a News Corp. shareholder would love to see that."

Investors likely will give News Corp. time to work on the project, being that its shares are up 18% this year. It easily has outperformed big media rivals Time Warner ( TWX) and Viacom ( VIA), which both have fallen 8%.

News Corp. also has outshined big-cap Internet stocks, including Google, Yahoo! ( YHOO) and ( AMZN).

"It is, of course, a fine line," says Lanctot, who does business with MySpace, of the plan to pursue ad dollars. "Do you charge an established record company, but not an indie band? How about an independent label?"