The Supreme Court ruled unanimously yesterday that a defendant has a constitutional right to present evidence about the way police secured his confession.

Acting in a murder case, Crane v. Kentucky, the justices said a trial court must allow a defendant to present to the jury facts surrounding his confession, including techniques used by police to obtain it.

The case involved Major Crane, who killed a clerk during a liquor store robbery in 1981. The court did not overturn his conviction but returned the case to lower courts to determine whether failure to allow his testimony was harmless error.

The ruling reversed the Kentucky Supreme Court, which had ruled that once a confession is determined by the trial court to be voluntary, evidence supporting that finding cannot be presented to the jury for any other purpose.

The Supreme Court also ruled, 8 to 0, that federal courts have broad authority to review the government's methods for determining Medicare reimbursement rates.

The decision in Bowen v. Michigan Academy of Family Physicians upheld a lower court decision that the Department of Health and Human Services must give family doctors in Michigan equal treatment with specialists in setting Medicare rates.

The justices rejected Reagan administration claims that granting federal courts such power would cause a flood of lawsuits.

In other matters, the court:

*Refused to force cable-television operators to carry all local television signals of their systems, letting stand a ruling that struck down the Federal Communications Commission's "must carry" rules.

*Agreed to hear the appeal of a Florida death-row inmate who says the state's capital punishment law is being applied in a racially biased way.

*Refused to let Bernalillo County, N.M., continue using a county seal found to be too religious. The seal features a cross and a Spanish motto meaning "With This We Overcome."

*Said it will study in a California case whether state and local governments may regulate high-stakes bingo games and other gambling operations on Indian reservations.

*Let stand a ruling in an Alabama case that unions may be sued for failing to oppose racial discrimination at businesses where they represent employes.