A unanimous Supreme Court ruled yesterday that Internal Revenue Service agents cannot enter a taxpayer's office without a search warrant merely because the taxpayer is a corporation rather than flesh-and-blood.

Tax experts told a reporter the decision is significant because it is a relative rarity for the court to curb the powers of the agency in enforcing the tax laws.

The experts said that the impact of the decision in the real world of collecting taxes from corporations probably will be small, partly because IRS agents - like police officers - will be able to get warrants as needed from judges.

In addition, the case was an esoteric one involving, among other things, the seizure of a four-door Stutz automobile valued at $100,000 and five other "collector's" cars - two more Stutzes, two Rolls-Royce Phantoms and a Jaguar.

Because the IRS seized the cars on public streets and parking lots in Salt Lake City and Los Angeles, the Tenth U.S. Circuit Court of Appeals held - and the high court agreed - that the agency did not need warrants.

But the 9-to-0 opinion by Justice Harry A. Blackmun reversed a holding by the lower court that the IRS did not need a warrant when it entered the office of a corporation, G.M. Leasing Corp. of Salt Lake (unconnected with General Motors Corp.).

The entry violated the constitutional guarantee that the people will "be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures," the court ruled.

The company was an alter ego for George I. Norman Jr., who was sentenced to four years in prison for misuse of a bank's money, fought the sentence all the way to the Supreme Court, lost, surrendered to a U.S. marshall only to disappear immediately after a ruse, and became - and remains - a fugitive.

At the time of his disappearance - March, 1973 - the IRS figured he owed taxes for 1970 and 1971 of 951,410. He had given the agency a check for $405,125, but it bounced or, in the court's elegant phrase, "evidently was dishonored."

Failing to get Norman's wife to pay up, IRS agents seized the cars, which were listed to the alter-ego corporation, and then went to the firm's offices, consisting of a cottage-type building and a garage.

They ordered a locksmith to take the lock off the garage, which turned out to house yet another Stutz. But on entering the building agent Bert Applegate decided it could be a residence, left without taking anything, and had the door lock replaced.

A tipster told the agents that the night after they left, Norman's son drove the Stutz away and there had been "activity" in the cottage.

The IRS waited two days before they re-entered, without a warrant. This delay deprived the agency of a claim that it lacked time to get a warrant. Chief Justice Warren E. Burger emphasized in a concurring opinion. The agents then seized books, records and other property.

The government claimed, but the court denied, that furtherance of tax enforcement justifies warrantless intrusions as shown by the history of common law and the laws in several states before the Bill of Rights was adopted.