ASHINGTON, April 21 — The Supreme Court decision three years ago that reaffirmed the Miranda ruling removed a cloud over a Warren Court landmark but also created a kind of echo effect of conflicting rulings in the lower federal courts.

In accepting a government appeal today, the court agreed to examine the continued validity of a series of its post-Miranda decisions about where to draw the line on the use of evidence.

As the Supreme Court grew increasingly conservative in the 1970's and 1980's following its 1966 decision in Miranda v. Arizona, it issued rulings that have permitted prosecutors to use physical evidence obtained by the police as the result of statements made by suspects who were not given proper Miranda warnings. Some lower-court judges, though, took the court's 2000 ruling that affirmed Miranda to mean that such evidence was no longer allowed to be used.

The justices said today that they would review a decision by the federal appeals court in Denver, which ruled last September that physical evidence — a gun, in this case — discovered as a "fruit" of a Miranda violation could no longer be introduced as evidence at trial despite Supreme Court rulings to the contrary. The appeals court's reasoning was that the premise of the earlier cases was "fundamentally altered" when the Supreme Court declared three years ago in Dickerson v. United States that the warnings set out in Miranda were not simply "prophylactic" measures to insure that confessions were voluntary, but were directly required by the Fifth Amendment's protection against compelled self-incrimination.

The earlier cases, principally Michigan v. Tucker in 1974 and Oregon v. Elstad in 1985, were based on the premise that a Miranda violation was not a constitutional violation as long as the suspect's statements were voluntary, the United States Court of Appeals for the 10th Circuit noted in its opinion. That court ordered suppression of a pistol that police found in the Colorado Springs home of a suspect, Samuel F. Patane, whom they had just arrested for violating a domestic violence restraining order. The police asked Mr. Patane about the gun, and he described its location without having first received the Miranda warnings.

"Because Dickerson now concludes that an un-Mirandized statement, even if voluntary, is a Fifth Amendment violation," the evidence had to be suppressed, Judge David M. Ebel wrote for the appeals court.

But that was a misunderstanding of the Dickerson decision, Solicitor General Theodore B. Olson told the justices in the government's appeal, United States v. Patane, No. 02-1183.

Rather than rejecting the notion that physical evidence derived from a Miranda violation was admissible, Mr. Olson said, the Supreme Court in its 2000 decision incorporated that concept into its conclusion that because the Miranda decision was limited to actual statements, it had not imposed an unduly difficult burden on law enforcement.

Further, Mr. Olson said, while one purpose of the Miranda rule was to "guard against the use of unreliable statements at trial," physical evidence like the gun in this case "undoubtedly constitutes reliable, trustworthy evidence."

The debate among judges over the implications of the Supreme Court's ruling in the Dickerson case has been spreading through the lower courts, leading to conflicting rulings "on an important constitutional issue that arises with regularity," the government's brief said. This assertion prompted a response from Mr. Patane's lawyer, Michael G. Katz, the federal public defender in Denver, who said in his brief that "the question arises frequently because the police often violate the constitutional requirements of Miranda."

The decision in Dickerson v. United States, written by Chief Justice William H. Rehnquist, declared unconstitutional a federal law, known as Section 3501, that Congress passed shortly after the Supreme Court issued its 1966 Miranda decision. Section 3501 sought to overrule the Miranda decision by restoring "voluntariness" as the test for the admissibility of a confession, without a requirement that the suspect receive any particular warnings or advice. Congress cannot overturn a constitutional ruling by the Supreme Court and the Miranda decision had been such a ruling, Chief Justice Rehnquist wrote.

There were also these developments at the court today.

Automobile Search

The court agreed to decide the circumstances under which the police can search a car following the arrest of a recent occupant outside the car.

In this case, an appeal by the state of Arizona, the police followed Rodney J. Gant to his home to serve him with an arrest warrant. When Mr. Gant got out of his car to walk toward his house, an officer arrested him. The police then searched Mr. Gant's car and found cocaine and drug paraphernalia.

The Arizona Court of Appeals ordered the evidence suppressed on the ground that unless a suspect was aware of the presence of the police before leaving a car the vehicle cannot be searched under those circumstances without a search warrant.

In its appeal, Arizona v. Gant, No. 02-1019, that this subjective inquiry about a suspect's awareness introduced too much uncertainty into the law enforcement practice of a "search incident to arrest." The Supreme Court affirmed the "search incident" in the context of automobiles in a 1981 decision, New York v. Belton. But since then, several state and lower federal courts have held that for such a search to be reasonable within the meaning of the Fourth Amendment, a suspect has to have been aware of the police presence before leaving the car.

Age Discrimination The court agreed to decide a "reverse discrimination" age case, on the question of whether the law that prohibits discrimination on the basis of age also prohibits practices by employers that treat older workers more rather than less favorably.

The case, General Dynamics Land Systems, Inc. v. Cline, No. 02-1080, grew out of a collective bargaining agreement between General Dynamics and the United Auto Workers. The agreement terminated health benefits for retired workers, except for those who were at least 50 years old on July 1, 1997.

The protections of the Age Discrimination in Employment Act begin at age 40. A group of employees who were between the ages of 40 and 50 brought an age discrimination suit. The federal district court in Cleveland dismissed the suit on the ground that the law did not prohibit favoritism toward older workers. The United States Court of Appeals for the Sixth Circuit, in Cincinnati, reinstated the suit. The case has potentially broad implications for employee pension and benefit plans.