NEARLY HALF A CENTURY ago, on Feb. 15, 1933, an attempt was made on the life of President-elect Franklin D. Roosevelt. The assassin missed his target, but shot Chicago's mayor, Anton Cermak, who died on March 6 of that year. The killer, Guiseppe Zangara was indicted that day and pleaded guilty. He was electrocuted 10 days later, on March 20.

Legal scholars and commentators have recalled that case as the anniversary of the attempt on President Reagan's life approaches. On March 30 of last year, the president, his press secretary James Brady, a Secret Service agent and a District policeman were shot as the presidential party left the Washington Hilton Hotel. John W. Hinckley Jr. was arrested at the scene with the gun still in his hand. Dozens of witnesses saw him pull the trigger and he does not deny that he did so. The only issue for the courts to decide is whether Mr. Hinckley is not guilty by reason of insanity.

Even under the best of circumstances, this is not the kind of case that can be solved as quickly in 1982 as it would have been in 1933. But the two recent decisions by the U.S. Court of Appeals in this jurisdiction have introduced new complications that might delay the Hinckley trial for many months. In the first case, Mr. Hinckley's lawyers sought to exclude from evidence certain statements made by the defendant shortly after he was arrested and certain written documents that were taken from his jail cell. A three-judge panel of the court of appeals agreed with their contention that the evidence had been obtained in violation of Hinckley's constitutional rights and ruled that it could not be used to show that he was sane at the time of the crime.

The government has asked for a rehearing by the full nine-member bench, a process that could take many months. Either side, of course, could then ask the Supreme Court to overturn an adverse decision, and lawyers agree that a decision would not be reached in that forum until well into next year. Only then, two years or more after the crime was committed, could the trial begin.

The second recent court of appeals decision having an impact on the Hinckley litigation was handed down last Friday. In this case, Cohen v. U.S., the court overturned a District of Columbia law providing that persons acquitted of crimes by reason of insanity be automatically committed to St. Elizabeths Hospital. By a 2-to-1 vote, the judges held that a whole new civil commitment proceeding is required before such persons can be sent to a mental institution. The opinion also raised--but did not answer-- the question of which party has the burden of proof when insanity is the issue.

In the District, the defendant must prove he was insane at the time of the crime in order to be acquitted; in federal courts outside the District, the prosecutor must prove that the defendant was sane if he is to be found guilty.

Since the Cohen case holds that federal commitment standards must be followed in this city, many lawyers believe that the federal burden-of-proof standard must be used as well. It is expected that this issue will be raised at the Hinckley trial. If he is acquitted on the grounds of insanity, the government will then have to institute civil commitment proceedings--a burden it did not have until last Friday--or see him walk out of the courthouse door a free man.

That in case you wondered, is what the hangup and delay are all about.