THE WASHINGTON POST Thursduy, March 15, i !7 7 V  
NEW YORK, March 14ÛÓThe stock market was mixed in slackened trading today, registering little response to prospects of a Mideast peace treaty.</br></br>One of the few pockets of strength was the American Stock Exchange, where the market value index peached a five-month high.</br></br>The Dow Jones average of 30 blue-chip industrials listed on the / New York*Stock Exchange slipped 1.56 points^to 845.37, erasing some of its modest 4.07 gain on Monday and Tuesday. . \\</br></br>But the Amex index chalked up a 0.68-point advance to 170.83, continuing its recent strong advance. The index has climbed'20.25 points, or about 13 percent, since the start of 1979, moving- withinChailing distance of its peak to l|6.87 last Sept. 13.</br></br>exchange have been oil and gas issues, as well as some of the gambling stocks, which have heated up again lately after last yearÛªs feverish speculation and subsequent selloff.