The stock market, reflecting continued uncertainties on domestic and international fronts, turned in a mixed performance today in slow trading.

Helped by a late spurt of buying, the Dow Jones index of 30 industrial stocks posted a 2.68 gain to close at 812.54.

Almost 2 points of the modest gain in the Dow index came in the final half hour of trading. The blue chip indicator had been off by more than 3 points near the opening, gradually recovered then drifted in a narrow range for most of the session.

In the broader tally of all stock trades on the New York Stock Exchange, losing issues outnumbered gainers by a margin of 8-to-5 at the closing bell.

"I think it's a wait-and-see marker," said William LeFevre, and analyst at Granger & Co.

Among uncertainties weighing on the market are the extent of oil price increases which may come out of this weekend's meeting of the Organization of Petroleum Exporting Countries, difficulties in the Mideast peace talks and concerns about interest rates, inflation and slowing doemestic economy.

Big Board volume of 20.84 million shares was down from Wednesday's 22.48 million and the slowest trading of the week. Nationwide turnover in NYSE-listed issues, including trades in those stocks on regional exchanges and in the over-the-counter market, came to 24.10 million shares.

Some analysts also cited the weekly money supply report by the Federal Reserve as an additional reason for restraint Thursday. The report is traditionally watched as a signal of government monetary policy affecting credit, interest rates and the inflation fight.

Those figures, released after the 4 p.m. close of the NYSE, showed a $2 billion increase in the nation's basic money supply in the latest reporting week following declines in the three previous weeks. But many analysts said an increase of that magnitude had been expected.

Columbia Pictures finished the session up 1/8 at 22 1/8 when it resumed trading after being halted at 21 3/4 for several hours during the afternoon. The Columbia board of directors announced endorsement of a previously announced tendor offer for 20 percent of the motion picture company's stock at$24 a share. The offer came from Kirk Kerkorian, who owns 5 percent of Columbia and 48 percent of rival Metro-Goldwyn-Mayer. Kerkorian has said he wants the stock for investment only and does not intend to seek control of Columbia.

Other actively traded issues included Texaco, unchange at 24; Standard Oil of Indiana, up 3/4 to 54 3/8; 1/8 and Lucky Stores, down 1/8 to 14 3/4.

Standard & Poor's index of 400 industrial stocks rose .06 to 106.71 while S&P's 500-stock composite slipped .02 to 96.04.

The NYSE composite index lost .02 to 53.70.

On the American Stock Exchange. Resorts International Class A rose 1/2 to 25 as the most active issue. The Amex market value index declined .02 to 150.21. In the over-the-counter market, the NASDQ composite index gained .02 to 118.15. CAPTION: Illustration, no caption, The Washington Post