It was the first day of spring 1986, but Anthony ''Fat Tony'' Salerno's heart was not light. He was feeling hard-used by the government, which was indicting him on 29 counts of mail and wire fraud, extortion, conspiracy to commit murder, various gambling violations and violations of the Racketeer Influenced and Corrupt Organizations Act and was charging him with being ''boss'' of the Genovese crime family.

Furthermore, the government, using the Bail Reform Act of 1984, was trying to keep Salerno indoors, holding him without bail in preventive detention prior to trial. Salerno said this violated the Fifth Amendment due-process guarantee, and he got an appeals court to agree.

But now the Supreme Court has ruled against him, 6 to 3. So Salerno fell short of repeating the victory he won when an appeals court held that pretrial detention on the grounds of future dangerous behavior is ''facially'' unconstitutional as violative of due process. A facial challenge holds that no circumstances exist under which the Bail Reform Act could be valid.

The act allows a federal court to detain an arrestee if, after an adversary hearing in which the arrestee is protected by a panoply of rights, the government presents convincing evidence that no condition of release will reasonably ensure the safety of individuals or the community.

The appeals court sided with Salerno, saying that it is a basic principle of justice that a person's liberty may be restricted only for past actions, not anticipated future actions. But that principle is more problematic and porous than the appeals court suggests.

The appeals court acknowledged that pre-trial detention is permissible after certain kinds of probability judgments, as when a defendant is found to be likely to jeopardize the trial process by intimidating witnesses or fleeing from trial. Such findings involve anticipations of behavior, predictive judgments not different in principle or complexity from the judgment to detain someone like Salerno on the grounds of future dangerousness.

The government moved to detain Salerno after he was indicted. An indictment involves the language of probability: there is probable cause to believe that an offense has been committed and that the indicted person committed it. And it is crucial to the use of the 1984 act in this case that Salerno was indicted not just for committing a crime, or even a lot of crimes, but for being an important participant in a complicated criminal organization with a peculiar momentum that makes certain anticipations reasonable.

When the district court sided with the government against Salerno, it noted that ''the activities of a criminal organization such as the Genovese family do not cease with the arrest of its principals. . . . When business as usual involves threats, beatings and murder, the present danger such people pose in the community is self-evident.'' So in Salerno's case there was no capriciousness or claim of clairvoyance involved in the expectation that a member of a criminal organization will continue to further its activities.

Still, in the Supreme Court, Justices Marshall, Brennan and Stevens dissented. Marshall, joined by Brennan, argued that the 1984 act is analogous to a hypothetical law imposing a dusk-to-dawn curfew on unemployed people because much violent crime occurs after dark and much of it is perpetrated by unemployed people. But the 1984 act involves a narrow, rigorously regulated kind of prediction that is particularly relevant to such people as Salerno (who, since this case began, has been convicted and sentenced to 100 years in prison for mob activities).

Chief Justice Rehnquist, joined by White, Blackmun, Powell, O'Connor and Scalia, conceded the ''general rule'' that government cannot detain a person prior to a judgment of guilt in a criminal trial. But Rehnquist cites numerous exceptions when the requirements of community safety outweigh an individual's interest in liberty. These exceptions involve the exigencies of war or insurrection, certain kinds of juveniles, some aliens facing deportation proceedings, some mentally unstable individuals and, to repeat, arrestees thought likely to jeopardize the trial process.

Marshall rightly notes that there is something at least problematic about the 1984 act's assertion that the act shall not be ''construed as modifying or limiting the presumption of innocence.'' But there is nothing novel about legal provisions (e.g., requirements for posting bail) that clearly proclaim that the presumption of innocence is compatible with changes in the rights of individuals as a result of arrest and indictment. That presumption must be balanced against probability judgments relevant to the community's interest in safety.