WASHINGTON — As federal regulators take their first tentative steps toward policing the wild west of medical information online, pharmaceutical companies are pressing their case to market drugs via Google, Twitter and other Web sites.

The Food and Drug Administration will convene a two-day meeting beginning Thursday to hear the drug industry's position on Internet marketing. The agency has agreed to consider developing rules for online advertising after companies complained that the current guidelines for traditional media — which require a detailed list of possible side effects — have left them hamstrung on the Web.

An estimated 83 percent of Internet users search for health information online, according to a recent survey from the Pew Research Center.

A few drugmakers have begun trying to reach patients via social networking sites like Facebook and YouTube. But overall the industry's online presence trails other sectors, including retail, financial services and computer makers.

In the first half of 2009, pharmaceutical companies represented just 4 percent of the $10.9 billion spent on online advertising, according to a report from PricewaterhouseCoopers.

Industry observers say companies have largely steered clear of the Web for fear of running afoul of FDA regulators, who have not defined the rules of operating online.

In a public statement announcing the meeting, the FDA acknowledged that "emerging technologies may require the agency to provide additional guidance." But some industry experts worry the FDA's rule development process — which often takes years — cannot keep pace with online innovation.

"What's happening is these new media are emerging at an increasingly rapid rate, and are being regulated by an agency that moves very slowly," said attorney Mark Senak, who advises drug companies as a consultant for communications firm Fleishman-Hillard. "In essence, you have a regulatory communication crisis developing."

The vast majority of the pharmaceutical industry's roughly $4.5 billion in annual marketing is still spent on traditional TV and magazine advertising, where the rules are clear: all ads that mention a drug must provide a balanced picture of its risks and benefits.

The requirement to disclose risk information demands those long lists of side effects heard during TV and radio spots, as well as the large blocks of small print seen in magazine ads.

When drug companies have tried to adapt such ads to the abbreviated language of Google and Yahoo, they've run into trouble. In April, the FDA fired off warning letters to Pfizer Inc., GlaxoSmithKline PLC and a dozen other drugmakers for search engine ads that did not mention drug risks.