ASHINGTON, Nov. 9 - The Supreme Court ruled on Tuesday that driving under the influence of alcohol, even when serious bodily injury results, is not a "crime of violence" for which an immigrant can be subject to automatic deportation.

The unanimous opinion, written by Chief Justice William H. Rehnquist, rejected an interpretation of the law advanced by both the Bush and the Clinton administrations. The decision opened the door for a Haitian immigrant who was deported under that interpretation two years ago to return to his family in Miami.

The immigrant, Josue Leocal, was a lawful permanent resident who had lived in the United States for 20 years when he was deported for having committed an "aggravated felony" - driving while drunk, running a red light and injuring two people. He pleaded guilty to violating Florida's drunken-driving law and served two years in prison.

While he was serving his sentence, the Immigration and Naturalization Service began proceedings against him, and an immigration judge found him deportable. The Board of Immigration Appeals upheld the order, as did the United States Court of Appeals for the 11th Circuit, in Atlanta.

The Supreme Court accepted Mr. Leocal's appeal, Leocal v. Ashcroft, No. 03-583, because courts around the country had issued conflicting rulings on whether drunken driving that results in injury or death fits within Congress's definition of a "crime of violence."

In 1988, Congress made noncitizens subject to automatic deportation after conviction for an "aggravated felony," defined to include crimes of violence. Congress subsequently provided two basic definitions of "crime of violence": an offense that includes "the use, attempted use or threatened use of physical force" and any other felony that involves the "substantial risk" that physical force "may be used."

Like most state drunken-driving laws, the Florida statute does not require proof that the driver acted intentionally, or had any particular mental state. The Bush administration told the justices that the use of force need not be intentional to bring an offense within the definition of a crime of violence. "When a drunk driver causes serious bodily injury with his vehicle, he has necessarily used physical force," the administration's brief maintained.

But Chief Justice Rehnquist said this was not a natural meaning of the word "use." Noting that "when interpreting a statute, we must give words their ordinary or natural meaning," he said, "While one may, in theory, actively employ something in an accidental manner, it is much less natural to say that a person actively employs physical force against another person by accident." The word "use," he continued, "most naturally suggests a higher degree of intent than negligent or merely accidental conduct."

The chief justice, who is undergoing treatment for thyroid cancer, was not on the bench on Tuesday; he is working at home.

He also wrote in the opinion that the second definition - a felony that includes a "substantial risk" of using physical force - did not logically apply to drunken driving either.

Congress was referring not simply to the possibility that conduct would result in a possibility of harm, he said, "but to the risk that the use of physical force against another might be required in committing a crime." He gave the example of burglary, which he explained "involves a substantial risk that the burglar will use force against a victim in completing the crime."

This was not the first time the court has had to interpret a simple and seemingly straightforward word like "use." A decision in 1995 rejected the government's interpretation of a law that imposes a mandatory prison sentence on anyone who "uses" a gun in connection with a drug crime.

The defendant in that case, Bailey v. United States, had a gun in a bag in the locked trunk of his car. The court held unanimously that the word "uses" meant "active employment" of the gun during the crime, not simple possession in a place that was not readily accessible.

Mr. Leocal, whose wife and children are United States citizens, was represented on a pro bono basis by the law firm of Kind & Spalding. A number of other aliens either facing deportation or recently deported will benefit from the court's decision, as well.

With those in Mr. Leocal's position having prevailed in some federal circuits and not in others, there was no estimate Tuesday of the number of people who might be affected.

Nationally, more than 79,000 immigrants were deported last year as "criminal aliens,'' government figures show. More than 8,000 of them were legal permanent residents.

The section of the law that the Supreme Court interpreted Tuesday deals only and explicitly with aggravated felonies deemed "crimes of violence." The decision will not assist aliens facing deportation under other sections of the immigration law for other offenses like misdemeanors.

However, Ira Kurzban, a prominent immigration lawyer in Miami, said the decision would affect immigrants across the country who face deportation for committing "crimes of violence," particularly those with appeals pending before the United States Court of Appeals for the 11th Circuit.

"It's going to make the difference between people getting deported or not getting deported," said Mr. Kurzban, whose law firm is handling three or four deportation cases he believes will be affected by Tuesday's decision. "It's going to have an immediate and significant impact on a large number of cases."

Lucas Guttentag, director of the American Civil Liberties Union's immigrant rights project, called the decision "a reminder of the critical role of the courts in reviewing executive-branch decision-making."