The Supreme Court ruled yesterday that a federal law originally aimed at combating mobsters may be used against a wide array of fraudulent activities having nothing to do with organized crime.

As a result, businesses throughout the country now are liable for paying triple damages to persons who successfully bring a civil suit under the Racketeer Influenced and Corrupt Organizations (RICO) Act.

The 1970 law has increasingly divided federal courts across the country and led to what has been called an "explosion" of litigation, including cases against American Express Co., E.F. Hutton & Co. and Lloyd's of London. In addition, the mere accusation of "racketeering" has proven to be a powerful inducement to out-of-court settlements.

The Reagan administration and American business representatives had argued for a narrow interpretation of the law. Instead, the high court reversed a ruling by the 2nd U.S. Circuit Court of Appeals that established specific requirements for a RICO civil suit.

RICO, the court said, may be used to reach "both legitimate and illegitimate enterprises." While recognizing that the law "is evolving into something quite different from the original conception of its enactors," the court said it was not for the judiciary to limit the application of the broadly worded statute.

Justice Thurgood Marshall, writing a dissent joined by three other justices, said the court's decision "quite simply revolutionizes private litigation."

Legal experts said RICO is now likely to be used in ever more commercial cases because of its liberal definitions of the words "pattern" and "racketeering activity." "Pattern" requires at least two acts of racketeering committed within 10 years.

"Racketeering activity" includes various offenses associated with organized crime such as gambling, extortion, murder, kidnaping, bribery and narcotics trafficking. But the term also includes frauds committed by mail or telephone, or involving securities or bankruptcies.

The division found in the lower federal courts was reflected in the two cases at issue yesterday, which had reached the Supreme Court from Chicago and New York with opposite results.

In Sedima, S.P.R.L. v. Imrex Co. the court reversed, 5 to 4, a narrower reading of the statute last year by the 2nd Circuit in New York.

The case involved a joint venture between Sedima, a Belgian corporation, and Imrex Co., a New York concern, to provide missile parts to NATO and split the profits.

The partnership soured, however, after Sedima alleged that Imrex president Gidon Armon and his son Jacob, another officer of the company, cheated Sedima by sending inflated bills and charging for nonexistent expenses.

A federal district court in New York dismissed Sedima's RICO suit and was affirmed by the 2nd Circuit.

That court held that a civil RICO suit could be brought only against a person with a prior criminal conviction associated with racketeering. It also ruled that Sedima had to demonstrate an injury "different in kind" from the injury caused by the prior offense -- an injury caused "by an activity which RICO was designed to deter."

In a 21-page opinion by Justice Byron R. White, the Supreme Court reversed the 2nd Circuit and said none of the requirements it imposed were in the statute.

The high court, quoting from the law, said RICO "makes it unlawful for 'any person' -- not just mobsters" to use money, acquire control, or conduct an enterprise "through a pattern of racketeering activity."

The court also rejected claims that persons and businesses found guilty under a civil RICO complaint will be tainted by charges of racketeering.

"As for stigma, a civil RICO proceeding leaves no greater stain than do a number of other civil proceedings," it said.

Marshall, in dissent, said the decision "validates the federalization of broad areas of state common law of frauds, and it approves the displacement of well-established federal remedial provisions."

A person or company now can be guilty of racketeering and subject to triple damages for the "mere two instances" of committing fraud through the mail or wire within 10 years, Marshall wrote.

The decision, he added, "virtually eliminates decades of legislative and judicial development of private civil remedies under the federal securities laws," because plaintiffs who would have trouble suing under those laws can instead sue under RICO.

The majority opinion was signed by, in addition to White, Chief Justice Warren E. Burger and Justices William H. Rehnquist, John Paul Stevens, and Sandra Day O'Connor.

Marshall's 24-page dissent was joined by Justices William J. Brennan Jr., Harry A. Blackmun, and Lewis F. Powell Jr. Powell also filed a separate dissent saying that "it defies rational belief, particularly in light of the legislative history, that Congress intended this far-reaching result."

In a second case, American National Bank and Trust Co. of Chicago v. Haroco Inc., the court upheld a decision by a federal appeals court in Chicago saying that RICO could be used by a borrower of a bank loan who alleged he was fraudulently charged excessive interest rates.

The case began in 1983 after a district court in Illinois dismissed a RICO suit brought by several businesses that had borrowed millions of dollars betweeen 1979 and 1981 and claimed to have been defrauded by the American National Bank and Trust Co. of Chicago.

The borrowers claimed that the bank was guilty of violating RICO because although it had claimed to set interest fees on the loans according to the prime rate, it had actually misrepresented the prime rate and charged excessive interest.

The 7th U.S. Circuit Court of Appeals in Chicago reversed the district court, ruling that it erred in holding that a RICO case could be brought only if the businesses could show evidence of injury "distinct" from their fraud claims.

The Supreme Court in a three-page unsigned opinion yesterday affirmed the appeals court and said that it is unnecessary to show that the plaintiff suffered a distinct injury.

Marshall dissented, citing his opinion in Sedima.

Although both cases decided yesterday concerned the narrower issues of what restrictions could be imposed on plaintiffs bringing civil RICO suits, the stakes were higher.

Legal scholars had observed beforehand that the justices could effectively kill civil RICO litigation by adopting a prior-conviction requirement or sharply curtail its effectiveness by requiring a separate injury distinct from that caused by the prior offense.

The RICO legislation originated in 1967, when a presidential commission recommended legislation to curtail organized crime. After numerous attempts, Congress passed RICO in 1970. Modeled after antitrust laws, it provided for triple damages in civil lawsuits as a way of encouraging "a private attorney general."

At issue before the court was the statute's language making it illegal for a person or business to conduct its affairs "through a pattern of racketeering activity." In recent years, that provision was increasingly employed in frauds not generally associated with organized crimes.

According to an American Bar Association survey cited by the Supreme Court, 270 civil RICO cases have been filed in federal courts since the 1970s. Last year, the courts had decided 43 percent of them. The year before, they had decided 33 percent, and in 1982, they had ruled on 13 percent.