Twelve jurors and 12 alternates were chosen yesterday to decide the guilt or innocence of 12 Hanafi Mulsims charged with murder, kidnaping and related offenses stemming from the taking of 149 hostages at three Washington buildings last March.

The jurors and alternates were sworn in by Judge Nicholas S. Nunzio at 5:10 p.m. after an exhaustive screening process that began last Wednesday and included an unusual Saturday session.

Nunzio promptly ordered the names, ages, addresses and other information about the jurors placed under court seal "for their security."

To speed the selection process, Nunzio directed U.S. marshals to provide lunches for all the vineremen in the main hall of the Pension Building, where the proceeding was conducted. The marshals brought in 120 hamburgers and french fries, soft drinks and apple pie from a nearby fast-food store. The cost was $212.40, according to court officials.

When the swearing in had been completed, the judge ordered the jurors and alternates sequested at an undisclosed location under guard by marshals. In response to requests from defense attorneys, he directed the marshals to remove all crime news from newspaper and magazines the jurors might see during the trial, which is expected to take as long as 10 weeks.

Nunzio also ordered marshals to be especially careful about television broadcasts the jurors may watch. He said he wanted no repeat of an incident in whicha mistrial was declared in the first trial of Maryland Gov. Marvin Mandel on political corruption charges after jurors saw a television bulletin about jury tampering in that case.

The trial is scheduled to resume today with arguments on various defense motions. Opening statements about the alleged crimes are expected to begin Wednesday or Thursday.

Most of the jury selection process since Wednesday has concerned publicity about the crimes. Nunzio questioned the veniremen individually about whether they could decide the case on the evidence presented in court and the law as given by the judge, even though they had heard or read about the case.

The Hanafis are accused of taking over the international headquarters of B'nai B'rith, the Jewish servic organization, at 1640 Rhode Island Ave. NW: The District Building at 14th and E Street NW. and the Islamic Center at 2551 Massachusetts Ave. NW.

One person was killed at the District Building and several others were injured at the three locations.

Four men and eight women, all of them black, were chosen for the jury. The alternates are a five men, four of whom are black, and seven women, all of whom are black.