Two jurors in the trial of John W. Hinckley Jr. said yesterday that they argued ardently for conviction until the final hours of deliberation, believing that Hinckley suffered from mental problems, but knew what he was doing when he shot President Reagan.

The jurors, Nathalia L. Brown and Maryland T. Copelin, described Hinckley as a shrewd young man in search of fame and glory who manipulated his family into giving him attention and finally manipulated the jury into finding him not guilty by reason of insanity.

"I felt that he was guilty and I argued and argued the case," said Brown, 30, a machinery repairman for the Potomac Electric Power Co. "Everyone was going on the evidence. To me, the evidence wasn't strong enough to say not guilty. I felt he had a mental disturbance, but I felt he knew what he was doing" on the day Reagan and three others were shot outside the Washington Hilton Hotel.

Copelin, 50, a food services worker at Shadd Elementary School in Southeast Washington, said, "He was guilty all the time. I know from the evidence there is something wrong with Hinckley . But I don't think it's to the point that he didn't know what he was doing."

Brown and Copelin said two other jurors joined them in pressing for a guilty verdict at the start of the deliberations Friday. But, they said, they backed down and voted with the others to find Hinckley not guilty when they no longer could tolerate the tense, emotionally charged atmosphere of the deliberations and the separation from their families.

"My nerves were just so bad I couldn't take it no more," said Brown, a tall, slender woman, who complained that she was not even permitted to make a 15-minute supervised telephone call to her sister during the 4 1/2 days that the jury was sequestered.

"We were more prisoners than the prisoners. We had no newspapers, no televison, no telephone," Copelin said, adding, "We had to get out for our own sanity."

The 12-person federal jury--seven women and five men, 11 blacks and one white, a diverse slice of people from the middle- and low-income neighborhoods of the District of Columbia--began to speak more openly with reporters yesterday.

For nearly two months their lives were dominated by the trial in U.S. District Court here of the 27-year-old college dropout and son of a wealthy Colorado oilman on 13 charges stemming from the shooting of Reagan and three others on March 30, 1981.

Some of those who spoke with reporters yesterday echoed the thoughts of many who contended that the not-guilty verdict was virtually inevitable once Judge Barrington D. Parker placed the burden on the prosecution to prove that Hinckley was sane.

Lawrence H. Coffey of Anacostia, 22, who helps set up banquets for the Hyatt Regency Crystal City hotel, said yesterday there was never a majority of jurors in favor of convicting Hinckley. On Monday morning, Coffey replaced 64-year-old Roy D. Jackson of Petworth as jury foreman, a job that, jurors said, Jackson really did not want.

However, juror Woodrow Johnson, 48, a garage attendant from Washington Highlands, told NBC news that initially the jury was split in half, with six who favored a verdict of not guilty by reason of insanity and six who were either undecided or felt Hinckley was guilty.

By Sunday morning, the fourth day of deliberations, a clear majority for not guilty began emerging after jurors reviewed Hinckley's sometimes cryptic writings and erratic travel patterns.

Coffey, Brown and juror Glynis T. Lassiter, 42, a custodian at American University who lives in Petworth, said yesterday that three major ballots were taken before the group came to its unanimous decision on the fourth ballot around 6:20 p.m. Monday.

Jurors interviewed said that during the 24 hours of deliberation, the jury zeroed in on the testimony of the defense and prosecution psychiatrists and Hinckley's writings and travel pattern.

Coffey and juror Virginia N. Smith of Woodridge, the 61-year-old wife of a retired city policeman, both said their decision was influenced by the fact that prosecution and defense psychiatrists alike testified that Hinckley was suffering from some mental disorder.

Both Coffey and Lassiter said they felt it was not normal for a young man--even a wealthy one such as Hinckley--to criss-cross the country with seemingly no purpose or particular destination.

Lassiter, interviewed after work in his apartment in the Petworth area of Northwest, said that the prosecution had failed to prove beyond a reasonable doubt that Hinckley was sane at the time of the shootings.

Copelin said she wished the jury could have found Hinckley guilty but insane--a verdict that does not exist in the D.C. and federal laws under which Hinckley was tried, or to have found him guilty on some counts and not guilty because of insanity on others.

But Brown said most jurors felt that "if he's insane, he's insane for the whole thing."

"He'll probably write a book," Copelin said. "This guy's not crazy, he's a genius."