(Reuters) - Microsoft Corp's new Bing search engine gained U.S. market share in its first month in operation but still trails dominant rival Google Inc, according to data released on Wednesday.

Bing, launched on June 3 but available to some users a few days earlier, took 8.23 percent of U.S. Web searches in June, up from 7.81 percent for Microsoft search just prior to its rollout and 7.21 percent in April, said Internet data firm StatCounter.

Google lost share slightly, dipping to 78.48 percent from 78.72 percent before Bing. Yahoo Inc, the perennial No. 2 in the market, rose to 11.04 percent from 10.99 percent.

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Bing's share peaked in the first week of June at 9.21 percent, falling away in the middle two weeks before coming back at 8.45 percent in the last week of June.

The results may give heart to Microsoft, which is investing heavily in its loss-making online services business and is refusing to cede the market to Google.

"At first sight, a 1 percent increase in market share does not appear to be a huge return on the investment Microsoft has made in Bing but the underlying trend appears positive," StatCounter Chief Executive Adohan Cullen said in a statement.

The world's largest software company may yet strike an online search partnership with Yahoo to make itself a credible competitor, but talk of such a deal has quietened down.

StatCounter, based in Dublin, says its data are based on 4 billion pageloads per month monitored through a network of websites. Other data research firms such as comScore are not expected to release figures on Bing's share until mid-July.

(Reporting by Bill Rigby and Georgina Prodhan; editing by Simon Jessop)