NEW YORK, JULY 27 -- The stock market posted modest gains in moderate trading today, drawing support from steady bond prices and a firm dollar.

The Dow Jones industrial average rose 8.61 to 2493.94. Advancing issues outnumbered declines by 4 to 3.

Broad market indexes rose. The New York Stock Exchange composite index rose 0.77 to 174.47. Standard & Poor's 500-stock index added 1.38 to 310.65. The price of an average share rose 18 cents.

Big Board volume totaled about 152,040,000 shares, compared with 158,393,830 on Friday.

The market's resilience "confounds everyone," said Larry Wachtel, analyst at Prudential-Bache Securities. "Bonds are dicey, the dollar has stopped climbing; by all definitions, the market should be going into a correction, and yet it continues to defy that reasoning," he said.

"We haven't had a major correction, but there's still a fair amount of skepticism," said Larry Greenwald, co-manager of equity trading at Sanford C. Bernstein & Co.

Rodd Anderson, vice president in equity trading at Shearson Lehman Bros. Inc., said a Dow retreat to 2450 this week is likely.

On the trading floor, Southern Co. was the most active NYSE-listed issue, slipping 1/4 to 24. Pinnacle West Capital followed, unchanged at 31 7/8. AT&T was third, rising 1/2 to 31 1/8.

Among other blue chips, Coca-Cola rose 1/4 to 47 1/8, Merck advanced 4 1/2 to 184 1/2, IBM jumped 1 1/8 to 162 3/8, USX rose 7/8 to 37, Eastman Kodak rose 5/8 to 88 7/8 and Union Carbide rose 1 1/2 to 28 3/4.