GOOGLE has surpassed Yahoo to become the most popular Website in the United States, according to comScore Inc's rankings by the number of unique monthly visitors.

Google Inc has long been the Internet's leader in search, but its audience has trailed Yahoo Inc's when counting other services such as e-mail and photo sharing.

April's numbers, which Internet tracking firm comScore plans to formally release, show Google on top for the first time.

The lead is tiny - 466,000 visitors out of about 141 million apiece. And while such measures are good as a gauge, they aren't known for precision. In fact, rival rankings from Nielsen Online already had Google as the top Web brand.

Still, comScore's finding is one more hint of Google's dominance over Internet pioneer Yahoo.

Jack Flanagan, comScore's executive vice president, said Google's dominance in search creates "a halo effect" that can boost its other services.

Google now has the Picasa online photo-sharing service, competing with Flickr from Yahoo. Google also has launched a site on finance, while its Gmail e-mail service keeps growing - and competing with Yahoo.

Google's US$1.76 billion purchase of YouTube in November 2006 gave it the leading video-sharing Website.

According to comScore, Google's unique US audience in April was 141.1 million, an 18-percent increase from the same month in 2007. Yahoo's audience grew 7 percent, to 140.6 million. Microsoft Corp was third at about 121 million.

That said, Yahoo still leads in page views, meaning visitors spend more time there or return more often. Many Google users make a simple search request and quickly go elsewhere. Yahoo had 33.6 billion page views to Google's 28.7 billion.