LOS ANGELES,Aug 14 (Reuters) - Search market leader Google Inc holds greater loyalty among its users, who conduct more searches a month than those on Yahoo! and Microsoft, new data issued on Friday showed, posing a challenge for the new team of rivals to Google.

While Yahoo! Inc and Microsoft Corp lag far behind Google in overall search share, their combined search penetration of 73 percent is not far behind Google, at 84 percent, according to research house comScore, Inc.

Yet Google searchers conduct an average of 54.5 searches a month -- about double the number of searches that Yahoo! and Microsoft users conduct combined. They search on average 26.9 times a month, comScore reported.

ComScore also found that Google searchers have the most loyalty, making nearly 70 percent of their searches on Google sites. People who use Yahoo! and Microsoft sites combined search there about 33 percent of the time and also use Google heavily.

While Yahoo! and Microsoft, which inked a 10-year Web search deal in July to counter Google, still look up to their rival in terms of market share, they have a "real opportunity to make headway given that nearly three-quarters of all searchers conduct at least one search on these engines every month," said comScore analyst Eli Goodman.

"The challenge will be to create a search experience compelling enough to convert lighter searchers into regular searchers which is generally easier than converting new users," Goodman said in a statement.

If they were able to match how many searches their users make with Google's searchers, Yahoo! and Microsoft, which recently launched its new Bing search engine, would command a more than 40 percent market share, Goodman added.

Google dominates the U.S. core search market with a 65 percent share of searches in June, compared to a combined 28 percent for Yahoo! and Microsoft sites.

(Reporting by Laura Isensee; Editing by Richard Chang)