A major battle is shaping up on Capitol Hill over efforts to weaken an increasingly visible law that allows corporations to be sued for triple damages in fraud cases.

The target is RICO, the Racketeer Influenced and Corrupt Organizations Act. The law is frequently used in criminal prosecutions against organized crime, but it can also be applied in civil suits against private companies, a potent weapon that recently passed muster with the Supreme Court.

Major corporations -- led by those in insurance, banking, securities and accounting -- are lobbying Congress to make triple damage suits nearly impossible. Under the law, the suits must show a "pattern of racketeering" by proving that two separate acts of fraud have been committed during a 10-year period.

The Justice Department has expressed "serious reservations" about a bill sponsored by Rep. Frederick C. Boucher (D-Va.) that would require that a company be convicted of criminal charges before a civil RICO suit can be filed against it.

Deputy Assistant Attorney General John Keeney recently told a House subcommittee that such amendments would "virtually eliminate" private RICO suits. He also said the federal government has used the law to file civil suits against a Kansas bank and a Florida defense contractor accused of fraud.

Russell Mokhiber, head of a group called Citizens Coalition to Support and Defend RICO, called the statute "a strong anti-corporate crime law that works . . . . The reason that people are using RICO more is because there is more corporate crime and fraud in America today."

Another measure, being pushed by Sen. Orrin G. Hatch (R-Utah), would bar RICO suits that rely exclusively on mail fraud, wire fraud or securities fraud -- three of the most frequent causes of action. An aide to Hatch said the statute has "been stretched out of its original context" and been used in everything from divorce cases to a dispute within a synagogue. He also complained that "the label of racketeer . . . can be damaging to a business' reputation."

A spokesman for Boucher said the congressman has received complaints from numerous firms that have been sued under RICO, including a coal company in his home district. He said the current law "is being used to harass a lot of legitimate businesses."

COMPUTER CONFLICT . . . Another Virginia lawmaker, Republican Sen. Paul S. Trible Jr., has run into the Justice Department's opposition with his bill to outlaw the use of personal computers to promote child pornography.

Trible contends that electronic bulletin boards are being used increasingly to obtain obscene materials or advertise for sexual exploitation of children. His measure would make it a crime to use computers to transmit obscene material across state lines or advertise minors for sex.

Justice Department attorney Lawrence Lippe told a Senate subcommittee that the administration supports the specific provisions dealing with child pornography. But he said that banning the mere transmission of descriptive information about juveniles "would raise serious constitutional problems." Trible's bill would outlaw computer messages aimed at "encouraging," "offering" or "soliciting" sexual contact with a minor.

Barry Lynn of the American Civil Liberties Union said the measure is so broad that it would "criminalize teen-ager computer dating services. I've heard sometimes teen-agers who go out on dates do have sex." Lynn accused Trible of "grandstanding" on the issue and said the senator and his allies "want to stop consenting adults from talking about sex in ways they think is improper."

A spokesman for Trible said the senator is "trying to iron these things out" in discussions with Justice officials. He said few statistics are available but the FBI believes that computer pornography is a widespread problem.