NEW YORK, AUG. 23 -- The Dow Jones industrial average plunged 76 today in heavy trading, its third-worst performance this year, as stock markets worldwide continued to respond to the prospect of higher oil prices, inflation and war in the Middle East.

Many investors chose to lighten portfolios in both foreign and domestic accounts. Selling pressures were persistent in early trading and again in the last three hours, but traders said the selling was generally deliberate and orderly, and there was no sign of ''panic'' selling.

The Dow fell 76 points to 2484 in the first 50 minutes of trading in the wake of another 1,000-point sell-off earlier in the day on the Tokyo stock market, which suffered a two-day drop in value of 10 percent. Traders were also responding to another full-point drop in early bond trading.

Although two quick bursts of futures-driven program trading contributed to the sell-off at the opening bell, traders said it was liquidations by institutional investors, not index arbitrage, that was the major force behind the morning market.

In fact, index arbitrage was extremely difficult to execute in early trading because so many basket stocks were slow to open. After 15 minutes of trading, one-third of the 30 usually highly liquid blue chips in the industrial index were not yet trading. Moreover, the New York Stock Exchange's 50-point program-selling curb was activated 24 minutes into the session, and remained in place for the rest of the day. The program-selling curb mandates that program selling after a 50-point Dow loss may occur only after upticks in the basket stocks that make up program trades.

At the close, the Dow stood at 2483.42, down 76.73, its lowest close since July 6, 1989. Declines swamped advances by 11 to 1 on heavy volume of 255 million shares, the second highest volume this year.

With the Dow off 516 points from its peaks on July 16-17 -- a massive 17.2 percent decline in only 27 trading days -- market technicians busied themselves with determining whether today's slide marked a classic ''selling climax,'' when liquidations reach extreme levels under emotional conditions, exhausting the market's downside potential for weeks or even months to come.

But analyst Jerry L. Favors, who publishes the Jerry Favors Analysis from Worthington, Ohio, cautioned that, despite the seemingly ''sold-out'' tape, the market may still have a considerable slide ahead of it.

Favors, who has been bearish on the market for many months, has often warned of the potential for a new crash ''not unlike that of October 1987'' if the Dow goes below 2500. Today, the Dow violated that floor.

''I think we have a lot further to go on this move,'' Favors said.

Among Dow components, even the oil stocks today were not spared the uncertainties surrounding events in the Persian Gulf region. Texaco fell 3 5/8 to 60 1/8, Chevron lost 3 to 75 5/8 and Exxon dipped 1 3/4 to 49 5/8.

Among active issues, Philip Morris fell 1 5/8 to 41 3/8, Boeing lost 2 1/2 to 42 1/2, General Electric sank 1 3/4 to 58 1/2 and IBM dropped 2 1/8 to 96 7/8 Procter and Gamble lost 3.

MCI continued its descent after announcing a big write-off earlier in the week, shedding 1 1/4 to close at 31 3/4.

The Dow transports skidded 33.03 to 861.31, led down by shares in UAL, which lost 7 1/2 before closing at 92 1/2. The Dow utilities fell 5.10 to 191.71.

Among broad stock indexes, losses were also severe. The Standard & Poor's 500 plummeted 9.49 to 307.06, the NYSE Composite fell 5.34 to 168.88, the Value Line plunged 8.79 to 236.11, the Amex Market Value gave up 8.54 to 315.85 and the Nasdaq Composite was devastated for a 14.61 loss at 360.23.