Online search giant Google Inc. (GOOG) should be able to continue allowing rival advertisers to use the trademarks of well-known companies such as LVMH Moet Hennessy Louis Vuitton (MC.FR) as search keywords, according to a legal opinion prepared for Europe's highest court, released Tuesday.

"Google has not infringed trademark rights by allowing advertisers to buy keywords corresponding to registered trademarks," said the court's Advocate General Poiares Maduro.

However, Google may be liable for featuring content in its adwords program that directly violates trademarks, Maduro added.

Google is before the ECJ in connection with a French case where a number of companies including Louis Vuitton complained that Google had infringed their trademark rights.

Google currently allows other companies, often less well-known, to use trademarks of famous companies as keywords. When a user searches for one of these trademarked words the search engine will bring up rival products or companies selling counterfeits of the known brands under "sponsored links" alongside the actual search results.

The French court hearing the case, the Cour de Cassation, is asking ECJ to rule on whether trademark owners can legally prevent Google from selling the right to use their trademarks as keywords.

-By Mike Gordon, Dow Jones Newswires; +352 691 180 766; mgordon.dowjones@gmail.com (Peppi Kiviniemi contributed to this article)