At least a dozen major drug and device makers are under investigation by federal prosecutors and securities regulators in a broadening bribery inquiry into whether the companies made illegal payments to doctors and health officials in foreign countries.

In previous investigations, federal officials have charged that some companies made these kinds of payments to encourage doctors abroad to order or prescribe their products. In the United States, companies routinely hire doctors as consultants to market drugs and devices to their colleagues and other health professionals at medical conventions and small gatherings. Such consulting arrangements are legal in the United States as long as the companies do not pay doctors directly to write prescriptions for their products.

But in much of the rest of the world, doctors are government employees. And even consulting arrangements that would be considered routine in the United States might violate the Foreign Corrupt Practices Act, particularly if the payments are outsize or the arrangements are not disclosed to the governments.

Of even greater concern to prosecutors in the United States are unusually large payments made to foreign doctors who oversee the growing number of clinical trials that drug and device makers conduct abroad, according to Kirk Ogrosky, a former top federal prosecutor who now represents drug and device makers at a Washington law firm.