If the crisis in the Persian Gulf heats up, would U.S. securities and futures markets melt down?

Probably not, say most market professionals, although they disagree on just how sharp a backlash there would be on exchange floors and trading pits."If you had the outbreak of a sudden, major shooting war in the Middle East, I suspect that short-term, the market would go into a freefall, but I also wouldn't be surprised at all if it closed higher two or three days later," said Robert Kirby, chairman of Capital Guardian Trust Co. in Los Angeles.

Yale Hirsch, a market tracker who produces the Stock Trader's Almanac, predicts "if there's no shooting war or drawn-out impasse, we expect the Dow (Jones industrial average) to break through 3,000 in 1991."

But if the crisis ends badly, the average, a key stock market indicator, could sink to 2,000 next year, he said.

Federal regulators say they have contingency plans to head off panic in the markets - but what those plans are, they're not saying.

The Securities and Exchange Commission, which oversees the stock, bond and mutual fund markets, says it has developed plans for emergencies and has been in contact with the exchanges.

"But we don't discuss specific situations or specific contingency plans," said Brandon Becker, associate director of the SEC's Market Regulation Division.

Wendy Gramm, chairwoman of the Commodity Futures Trading Commission, who oversees futures markets for key commodities such as oil, has said the CFTC and other agencies have plans for dealing with market disruptions. But she also would not elaborate.

A CFTC insider said officials have plans to get in touch with the exchanges to coordinate information among the various markets.

But "do we have a plan so that if X happens we'll do this? No. Because I think whatever X we put down, or Y or Z, there'd be Q, R and S on top of that. We don't have a plan in that sense and we just don't think we can," said the source, who spoke on condition of anonymity.

The big question is whether the markets' reaction to bad news from the Gulf would be severe enough to force the exchanges or regulators to shut them down.

CFTC Commissioner William Albrecht has said a market closing would be "the last thing you really want to do" because of the need to determine prices and keep trading flowing.

The Chicago Mercantile Exchange has said it would stop trading stock index futures, futures contracts based on a range of stocks, if the New York Stock Exchange closed in the event of war.

However, the NYSE also isn't revealing its hand.

"I'm not going to say there's a plan in place or not in place until you know what's been presented to you," said Richard Torrenzano, an NYSE spokesman.

Even officials at the Merc decline to discuss the issue on the record, saying they didn't want to speculate on what they might do.

NYSE officials point to a series of "circuit-breakers" created since the 1987 stock market crash that would slow down forms of computerized program trading - often blamed for worsening stock market volatility or temporarily halt trading if the market plunged or skyrocketed 250 or more points.

Should there be a surge in buying, selling or volume "these circuit breakers would serve to slow the market down and give everyone a chance to assess what has taken place and make an investment decision," said Torrenzano.

Kirby, the Capital Guardian Trust chief and a member of the commission appointed by President Reagan to investigate the 1987 stock market crash, said a market halt "is the only fair way to handle this kind of situation."

But market shutdowns, except for the occasional power outage in New York or Chicago, are rare.

The NYSE shut down at the beginning of World War I, from July 31 to Nov. 28, 1914. That was largely because of fears that gold-hungry Europe would sell its securities in New York and take gold home, sparking a possible economic collapse in this country, said stock market historian Robert Sobel of Hofstra University.

The New York markets also shut for V-J Day at the end of World War II and after President Kennedy was assassinated.