A mid-session wave of buying carried the stock market to its third broad gain in a row in active trading today.

Analysts said the advance was aided by expectations of some favorable news when the government reports Thursday on the April wholesale price index.

The Dow Jones average of on Industrial stocke climbed 6.53 to 940.72 after a net advance of 7.20 Monday and Tuesday.

Since it touched a 15-month low a week ago Monday, the average has rebounded more than 26 points.

Gainers outdistanged losers by close to a 2.1 margin on the New York Stock Exchange.

Big Board volume increased to 23.33 million shares from 21.95 million on Tuesday.

Nationwide turnover in NYSE-listed issues, including trades in those stocks on regional exchanges and in the over-the-counter market, came to 26.92 million shares.

Standard & Poor's index of 400 industrials rose .61 to 110.70, and S&P's 500-stock composite index was up .53 at 99.96.

Airline stocks showed strength, with American Airlines up 1 1/2 at 12: TWA ahead 5/8 at 10 2/3, and UAL 3/4 higher at 22 3/4. UAL said it expected much better results in 1977 than it had last year.

The airlines' gains, coupled with strength in most rail issues, spurred a healthy 3.26 advance to 240.36 in the Dow Jones transportation average.

Another area of strength showed up at the American Stock Exchange, where the market value index rose .50 to 113.55, its highest level since the index was established in September 1973.

Boeing, which projected record earnings for the year after reporting sharply higher first quarter profits early in the week climbed 1 1/4 to 52 1/8.