NEW YORK, OCT. 28 -- An open rift is developing between the major financial exchanges here and in Chicago over who deserves blame for the chaos that erupted in the U.S. stock and futures markets on "Black Monday," when the Dow Jones industrial average plummeted a record 508 points.

The finger-pointing, particularly by officials of the Chicago Mercantile Exchange, is already shaping the first round of political debate in Washington over what reforms should be enacted in the wake of the worst stock market fall in U.S. history.

At stake, according to financial executives here and congressional sources in Washington, is the future of the Chicago Merc, which has profited during the last five years from the steady growth of trading in stock index futures.

Stock futures contracts, such as the Standard & Poor's 500 index contracts traded at the Merc, allow investors to speculate on the overall movement of the stock markets in New York. The contracts are used by some large institutional investors to hedge the risk of wild swings in stock prices.

The debate over stock futures pits the Merc against the powerful New York Stock Exchange and its members, who include the largest brokerages and investment houses in the country.

"I've seen a lot of name calling," said Rep. Dan Glickman (D-Kan.). "I've seen what I believe to be an unfair characterization against the futures markets by the New York Stock Exchange. Everybody's a loser in that battle."

At the heart of the debate is disagreement over the role played by stock futures, particularly the S&P futures traded on the Merc, in the massive selling that hit markets in both Chicago and New York on Monday, Oct. 19.

Some Wall Street executives believe that trading in stock futures accelerated the market's collapse that Monday. Attention has been focused on the role of so-called portfolio-insurance stock trading programs, in which large investors sell S&P futures "short" -- speculating that the overall stock market will go down -- to protect the value of their stock investments.

A massive wave of futures selling on Black Monday led the stock market's sharp decline, exchange officials in New York and Chicago agree. But they disagree over whether futures trading itself was the culprit, or whether the problem was exacerbated by delays in stock trading on the New York exchanges.

While futures prices in Chicago plummeted at an unprecedented rate that Monday morning, selling pressure on the NYSE was pent up because trading in dozens of individual stocks was delayed. The delay was caused primarily by an imbalance of sell orders, but some have criticized NYSE floor specialists for failing to take steps to open trading.

"The Chicago Mercantile Exchange acted as a pressure valve for the world that demanded a place to sell off some of its risks in the stock market," said Leo Melamed, the Merc's chairman. "The others took a great deal of time to open. The New York Stock Exchange took close to two hours before all of their stocks were traded, and until that time there was literally no other market except the Chicago Mercantile Exchange."

Richard Torrenzano, an NYSE spokesman, defended the exchange's performance. "We think the NYSE computer systems functioned very well, that the exchange market makers known as specialists did an absolutely superb job and were there trading when access to other markets was not available."

How the debate over Black Monday is resolved by regulators and legislators in Washington will determine the future structure of both the U.S. financial markets and the regulatory system that oversees them.

Yesterday, Securities and Exchange Commission Chairman David Ruder and Kalo Hineman, acting chairman of the Commodity Futures Trading Commission, met behind closed doors with members of the House securities subcommittee.

According to Rep. Edward J. Markey (D-Mass.), chairman of the subcommittee, Ruder and Hineman were asked to describe the behind-the-scenes events at their respective agencies on the days leading up to and including Black Monday, and their views about financial instruments such as stock index futures.

Markey is examining whether it makes sense to have two separate agencies regulating trading in stocks and stock index futures. But the CFTC is expected to resist any attempt to shift regulation of the stock index futures to the SEC. Sources said SEC Chairman Ruder apparently thinks one agency, the SEC, should regulate trading in stocks and stock index futures, a move the CFTC is expected to resist.

"I think everything is on the table right now," Markey said. "I think the relationships that existed between the exchanges and the regulators changed forever at 4 p.m. last Monday."

Markey said his subcommittee wants to ensure that "a safety net has been established ... so we don't get the kind of free fall that occurred last week."

Officials at the New York and Chicago exchanges are anxious to tell their side of the story on Capitol Hill.

After flying into New York today for meetings with the press and financial executives, Merc chairman Melamed will join John J. Phelan Jr., chairman of the NYSE, at a closed hearing Thursday in Washington before the Markey subcommittee.

Merc officials will also brief a number of other House members and senators while in Washington, according to Merc Vice President Charles Seeger, who works in the exchange's D.C. office. "We want to tell our story in this," Seeger said. "We are confident that when the facts and information are available, people will be pleased."

The Merc has lobbied aggressively in Washington in recent years and its political action committee has made extensive contributions to key oversight committee members in both houses. An earlier crisis in the silver market caused by the Hunt brothers' attempt to corner the market tested the Merc's clout on the Hill and with its regulators.

Still, the Merc's influence in Washington does not compare to the high profile of the NYSE and its members. The Merc has found itself on the defensive in recent days as politicians, journalists and others have focused on the role of computerized stock and futures trading programs in the s collapse. Merc officials have tried to emphasize the role of economic factors such as the country's trade and budget deficits.

"To say the crash was due to program trading or the futures market is completely ludicrous," said John F. Sandner, chairman of the Merc's board of governors.

Much is at stake for the Merc. In 1982, after three years of lobbying, the exchange persuaded its regulators, the CFTC, to permit S&P 500 index futures trading. Since then, the number of stock futures contracts traded annually on all exchanges has risen from about 5 million in 1982 to 26.5 million in 1986, with three-fourths of that trading through the Merc, according to Seeger.

Controversy over stock futures trading has also put pressure on the CFTC, a smaller regulatory agency often overshadowed by the SEC. The CFTC kept control over stock futures regulation in 1982 after a compromise was reached with John S. Shad, then the SEC's chairman.

Critics of the CFTC have said the agency has been too lax in its scrutiny of stock futures trading and its impact on other financial markets. Congressional sources said that consolidation of futures regulation between the CFTC and SEC will be given a close look in Congress.

CFTC Commissioner Robert Davis said he sees no evidence that a new regulatory structure is needed. "We are the expert regulatory agency {relating} to all futures markets. There's no functional logic to consolidation or alteration of the current regulatory structure, unless that's done across the board to all futures regulation" including oversight of futures trading in agricultural commodities."