Oct. 2 (Bloomberg) -- Microsoft Corp. Chief Executive Officer Steve Ballmer played down reports that the software maker may buy a stake in social-networking site Facebook Inc.

``We are so delighted to be the advertising sales partner for Facebook,'' Ballmer said today at a Microsoft advertising event in Paris. ``Everything else is just press, idle speculation.''

The company, the world's biggest software maker, is in talks to purchase as much as 5 percent of Facebook for $300 million to $500 million, the Wall Street Journal reported Sept. 24, citing unidentified people familiar with the matter. That would value Palo Alto, California-based Facebook at as much as $10 billion.

Microsoft has an ad agreement with Facebook in the U.S. Buying a stake may give Redmond, Washington-based Microsoft a deeper relationship with the startup and more opportunities to expand its own ad sales to compete with Google Inc.

Microsoft shares dropped 7 cents to $29.70 at 4 p.m. New York time in Nasdaq Stock Market trading. They are little changed this year.

Ballmer, 51, also said Microsoft will offer more software and online services that integrate ads as more businesses seek to attract clients over the Web. He spoke at a conference organized by Microsoft's digital advertising business.

``Looking five, six, seven, 10 years ahead, advertising will become 15, 20, 25 percent of Microsoft's business,'' Ballmer said. ``As much as people have bones to pick with advertising, people much prefer an advertising-funded experience to one they pay for.''

Ad Revenue

Microsoft boosted ad revenue by 21 percent to $1.84 billion in the fiscal year ended June 30, while Google's ad sales jumped 64 percent to $13.3 billion in the same period. Google handled five times as many Web search queries as Microsoft in August, according to ComScore Inc. in Reston, Virginia.

Teenagers and young adults have flocked to Facebook since the site expanded beyond university students a year ago, attracting advertisers that want to target users of a particular age or gender.

U.S. visitors to privately held Facebook more than doubled to 33.7 million in August from a year earlier, making it the 14th most popular site, according to ComScore. Visitors to News Corp.'s MySpace, the biggest social-networking site, increased 23 percent to 68.4 million.

To contact the reporter on this story: Rudy Ruitenberg in Paris at rruitenberg@bloomberg.net

Last Updated: October 2, 2007 16:24 EDT