The D.C. prison study commission yesterday voted for the second time to reject construction of a new prison in the District in favor of alternatives to incarceration, despite a personal appeal from Mayor Marion Barry that members reconsider their decision.

The vote on the motion to reconsider, however, was 9 to 6, closer than the 10-to-3 vote last month to reject prison construction. Some commission members said that this will not necessarily be the commission's final position.

"Next time we will get a majority," said commission member Joslyn Williams, president of the Metropolitan Washington Council of the AFL-CIO. He said three members of the 15-member panel will not vote for construction unless they are assured that the new prison will not be built in Ward 8.

The commission's recommendations are not binding on the city government. Some members argued that because the mayor and Congress have decided to build a prison, the commission should try to exercise some influence on the situation by analyzing possible sites.

"I voted for alternatives to incarceration , and probably will continue to do so, but I want to know where the possible prison sites are," said commission member William P. Lightfoot Jr. "No matter what we do, Congress is going to get a prison."

The commission then approved a motion from Lightfoot to hold three days of hearings on alternatives to incarceration and one day of hearings on potential prison sites. These hearings will be held on the four Mondays before the commission's previously scheduled Oct. 28 public hearing.

The Rev. Edward A. Hailes Sr., the commission's chairman, said after the meeting that the commission might change its mind after it hears from the public at that hearing.

Hailes, who as chairman did not vote on the original resolution, voted in favor of reconsideration yesterday. He said later that he had become convinced by the experts who had gone before the commission that "it is evident that we need to have more facilities."

Barry told the commission last night that, as a longtime supporter of alternatives to prison sentences, he had come only reluctantly to the conclusion that the city had to build a new prison to deal with crowding at its facilities.

There were 6,485 persons incarcerated yesterday in District facilities, which have a capacity of 5,640, Barry said, and the city foresees an increase of sentenced prisoners.

"The numbers are driving this discussion," he told the commission in his low-key appeal. "When it's all said and done, we are going to have to have more jail space."

Barry reversed his position this year, finally endorsing the idea of a new prison to be built in the District on federal land and using federal funds, after intense pressure from Sen. Arlen Specter (R-Pa.) on the issue. Specter has added $30 million in federal funds for the prison to the D.C. appropriations bill, due to be considered by the full Senate soon.

The District is under court order to reduce the inmate population at the D.C. Jail.

D.C. corrections director James Palmer told the commission yesterday, "They are coming in faster than we can let them out."

But some commission members argued at the meeting that they have not fully explored alternative programs available for dealing with offenders and that drug treatment for addicts would be a preferable way to deal with criminals who commit crimes to support drug habits.

Commission member Albert Long, who had voted for the original motion to reject prison construction, made the motion to reconsider.