The Surpeme Court opened its new term yesterday by announcing actions on a broad array of issues, including possible nuclear disasters, a "profile" of airborne narcotics couriers, prisoners' rights, and purported enslavement of Alabama lawyers.

Returning to the bench after a three-month recess, the justices set about two dozen initial cases for argument and decision by next June or early July. However, some of yesterday's most important actions were refusals to review decisions by lower courts.

In one such refusal, the court preserved a Nuclear Regulatory Commission policy that was called sharply into question in connection with the Three Mile Island episode. The policy, affirmed by the U.S. Court of Appeals here, declares that a 1969 environmental law doesn't require the NRC to consider the most dangerous class of nuclear accidents in licensing new reactors.

The cases accepted by the court for consideration include these: Narcotics

Since 1974, Drug Enforcement Administration agents, staked out at air terminals to intercept narcotics couriers, have used a behavioral "profile" to detect suspects. One such suspect, Sylvia Mendenhall, was stopped, searched, found to be carrying hidden heroin, and was convicted.

But in a ruling said by the government to pose a serious threat to its "major and highly successful program," the 6th U.S. Circuit Court of Appeals held that Mendenhall's Fourth Amendment protections against unreasonable searches and seizures had been violated.

A DEA agent stopped her after noting, among other things, that she was the last to leave a flight arriving in Detroit from Los Angeles, glanced about nervously in the deplaning area, and carried no luggage. Plea Bargaining

In a District of Columbia heroin case, the court granted a plea by Winfield L. Roberts to decide whether lack of cooperation with the federal government was a relevant factor in his sentence.

The prosecutor argued for -- and Roberts against -- imposition of consecutive sentences of one to four years after the defendant pleaded guilty to two counts of using a telephone in distributing heroin. The prosecutor prevailed.

In the U.S. Court of Appeals, dissenting Judge David L. Bazelon said that the case "raises a serious danger that future defendants may be punished by the sentencing judge if they do not accept the prosecutor's offer during the period of 'bargaining' over indictments and pleas." Magistrates

The court will consider a 7th U.S. Circuit Court of Appeals ruling that a federal judge can't decide whether to suppress illegally gained evidence on the basis of a record developed by a magistrate. Informants

In a case involving a 1972 robbery of a Norfolk, Va., bank, the court will decide whether the FBI violated a suspect's rights by use of statements from a cellmate who had agreed to act as a government informant. Miranda Rights

In 1976, Joseph D. Meehan confessed to a girl's brutal murder. But the Massachusetts trial judge ruled that the state hadn't shown that Meehan had waived his Miranda rights against self-incrimination.

The state's highest tribunal agreed, pointing out that Meehan was only 18, poorly educated, had consumed 12 beers and 24 Valium tablets, wasn't informed of his right to summon family or friends, and was told by police that a confession would help his defense. The state's plea for High Court review was accepted. Rejected Cases

The court's refusal to review most of the nearly 1,000 cases on its initial agenda left intact:

An Alabama system requiring lawyers, for inadequate fees paid by the state, to counsel indigents -- adults accused of crimes and juveniles -- at all proceedings affecting them. A divided state supreme court, while professing sympathy for the lawyers, rejected their claims that the system amounts to unconstitutional "involuntary servitude" and that the legislature knows that it deprives indigents of adequate counsel.

The California receivership of the 100,000-member Worldwide Church of God obtained by the state last January to stem alleged massive frauds by leaders of the sect of fundamentalist tithers.

The robbery-kidnapping convictions of Emily and William Harris, founders of the Symbionese Liberation Army, stemming from a 1974 episode at a sporting goods shop near Los Angeles; they drew sentences of 11 years to life, atop terms of 10 years to life for the kidnaping of Patricia Hearst.

The right of 15 widows to press a damage suit against Blue Diamond Coal Co. in connection with the deaths of their husbands in a 1976 disaster at a mine owned by a Blue Diamond subsidiary, Scotia Coal Co., at Oven Fork, Ky.

A Pennsylvania State University system barring participation in trustee elections by undergraduates while allowing it by alumni and members of private agricultural and industrial societies.

A Colorado requirement that driver's license applicants be photographed; the requirement had been challenged by a religious sect because its tenets forbid members to be photographed with their knowledge.

A Nebraska conviction of a woman for selling obscene movies. Claiming she was denied a fair trial, she said jurors have to be in the 21-to-70 age range but 19-year-olds can buy sexually explicit films.