A new study on top executives’ use of social networking tools shows that sites such as Facebook, Twitter and LinkedIn have made serious inroads in the C-Suite.

According to a survey of chief executive officers and other senior staff, two-thirds of respondents say online networks play an important role in deepening relationships with colleagues and clients. The study of 100 executives, conducted by public relations firm Margolis & Co. and the Young Presidents’ Organization, will be released later today.

Not surprisingly, business-oriented networking site LinkedIn is proving to be the most popular social network among the respondents. Some 75% of those surveyed say they use LinkedIn; Facebook attracts about 62% of this high-powered crowd (the respondents can list more than one site) and Twitter pulls in about 42% of those surveyed.

Simon Preston, chairman of YPO-WPO International, notes that executives who join a global professional association such as Young Presidents’ Organization are already hip to the benefits of networking.  And given that the members are, by definition, young, it stands to reason they’d embrace high-tech networking, too.

“Peer-to-peer idea exchange remains the core of our member experience,” Preston says. “Now, we’re looking at the next generation of social media, which will have many of the same features that have been so successful in Facebook and LinkedIn.

“It’s a phenomenon that is very much on our radar and key to our continued relevance for a future generation of young global business leaders.”

The study suggests social networking has infiltrated the business conversation in a meaningful way. Nearly 45% of respondents say social media topics surface in executive-level conversations “very often” or “often.”

That’s a fairly high level of interest considering LinkedIn launched in 2003 and Facebook only opened its platform to non-students in 2006.

“Nearly every company we surveyed has social media on their radar screen and their leaders understand the potential,” says Dan Margolis, president of  Santa Monica, Calif.-based Margolis & Co.

To be sure, executives in professional services and technology sectors tend to rally ’round social networking tools, according to the study. But 80% of respondents say their companies plan to invest more resources in social networking funding and staff in the next two years.

“We believe 2010 will be a turning point in the business to business sector,” Margolis says. “By this time next year, the landscape may be completely changed.”