A tentative jury of 16 men and women was chosen yesterday in the Middle sex Superior Court trial of Dr. Arif Hussain, a former resident at a Harvard affiliated hospital, for allegedly raping one Waltham Hospital patient and indecently assaulting another while he was a doctor at Waltham in 1978.

Kenneth Goldberg, one of Hussain's four defense atoms, said yesterday the trial could begin Friday or Monday. But chief defense attorney Thomas C. Troy said the selection process may take longer, since he can still challenge up to 18 proposed jurors.

"It's possible we could have to select a whole new group of jurors," he added.

Judge Andrew G. Meyer resolved one major pre-trial question by deciding to try Hussain on the charges of rape and indecent assault simultaneously, rejecting the defense's motion to separate the charges.

Another volatile issue early in the trial has been whether to admit as evidence Hussain's previous conviction in the 1980 rape of a nurse at Harvard-affiliated Brigham and Women's Hospital while Hussain was a resident anesthesiologist there.

Troy said Mcyer has decided this question but has instructed lawyers for both sides not to comment.

After Meyer denied several motions for dismissal of charges, filed by Hussain's attorneys, Meyer and attorneys Tuesday began questioning the original pool of 62 prospective jurors for prejudice or exposure the pretrial publicity. Challenges to the remaining 16 jurors will continue throughout the week.

Meyer also announced yesterday he will sequester the jury in a nearby Ramada Inn for the entire trial, which attorney predict could last several weeks. In an address to the jury yesterday, Meyer said that sequestering a jury during a trial, white unusual, is necessary in this case because of its extensive pre-trial publicity.

Meyer also strongly urged the jury members not to discuss the case among themselves during the trial.