Under pressure from Congress, Mayor Marion Barry and D.C. City Council Chairman Arrington Dixon said yesterday they would support significant changes in the city's criminal code intended to keep more repeat offenders in jail while they wait to stand trial.

One proposal would allow D.C. Superior Court judges to set high bonds to keep off the streets defendants charged with serious crimes and determined to pose a threat to the community, a practice specificially prohibited by the current law and one that civil libertarians claim would discriminate against the poor.

Another proposal would increase from 60 to 90 days the length of time certain suspects in criminal cases could be detained without trail, under pretrial detention laws. Prosecutors have been reluctant to invoke the federal and D.C. pretrial statutes because they say 60 days isn't enough time in which to prepare a criminal case.

A third change would permit judges five working days, instead of five calendar days, to decide whether to grant bail to defendants believed to be on probation or parole for other offenses. This proposal would give the court more time to check up on suspects who are arrested over the weekend.

Barry and Dixon announced their support for the changes, some of which had been proposed by council member David A. Clarke (D-Ward 1), after a meeting on Capitol Hill.

Those at the meeting included Sen. Alfonse M. D'Amato (R-N.Y.), who controls the city's purse strings as chairman of the D.C. Appropriations Subcommittee; Sen. Strom Thurmond (R-S.C.), chairman of the Judiciary Committee; Joseph E. diGenova, the principal assistant U.S. Attorney for the District; D.C. Police Chief Maurice T. Turner and H. Carl Moultrie I, chief judge of the D.C. Superior Court.

Earlier this week, Barry and Dixon were admonished by D'Amato to beef up efforts to put more criminals who have repeatedly committed violent crimes in jail this summer, even if it means keeping the courts open at night.

"We've identified 400 recidivist criminals and any one of them is responsible for as much as 6 percent of the burglaries committed in the city ," D'Amato said after the meeting yesterday. "We've got to get them off the streets. You just can't continue this revolving door."

Barry and Dixon indicated that 90-day emergency legislation to change the laws for detaining repeat offenders might be ready for consideration at the July 6 meeting of the City Council.

Clarke, chairman of the council's Judiciary Committee, introduced similar legislation to increase the time that suspects could be held without hearings or trials. His proposals were defeated in committee by a 3-to-1 vote last July.

Clarke, who is challenging Dixon for the Democratic nomination for chairman of the council, yesterday criticized Dixon for waiting until he was prodded by D'Amato to get behind changes in the pretrial detention legislation to make it more practical.

Clarke said city officials would be wiser to strengthen the hand of the courts and prosecutors in using the pretrial detention statutes than in relying on high bonds to keep potentially dangerous repeat offenders in jail until their trials.

"The rich--the John Hinckleys of the world--will be able to get out on bond if we used the cash bond approach," Clarke said. "To me, preventive pretrial detention is a better approach."

An official of the American Civil Liberties Union (ACLU) of the National Capital Area described the proposed changes in the criminal law as outrageous and claimed that D'Amato forced Barry and Dixon into supporting them.

"We already have a preventive-detention law, but what they want to do is for the judges to set very, very high money bonds that poor people can't reach and avoid any due-process hearing," said Leslie Harris, executive director of the ACLU.

"Unfortunately, the pressure that will be brought to bear by D'Amato may override the City Council's concerns," Harris said.

Barry and Dixon said that their proposals for changing the law are aimed at getting dangerous repeat offenders off the streets, and not creating greater hardships for poor people.

"We need greater flexibility in holding people who are a threat to the community," Dixon said. "There are poor people affected by crime who are getting robbed, raped and beat up. Their concern is to keep dangerous people out of the community."

Annette Samuels, the mayor's press secretary, said the proposed change in the law was not aimed at the community as a whole, but at dangerous repeat offenders.

Yesterday's one-hour meeting on Capitol Hill was called by D'Amato, who pledged earlier this week to "stop the revolving door" for criminals by trying to find more funds for the U.S. Attorney's office and helping the city to come up with more funds to keep its courts open at night if necessary.

At a press conference following the closed-door meeting, D'Amato said that Judge Moultrie agreed to appoint two special hearing officers to assist the court handling pretrial detention cases, at an annual cost to the District of $200,000.

D'Amato said the U.S. attorney's office has also promised to step up its efforts to get repeat offenders off the streets.

Barry has told D'Amato that the city would cooperate in this stepped up effort despite severe overcrowding in the city's prison complex at Lorton and at the D.C. Jail, where officials said there were nearly 500 more inmates this week than the 1,365 it was built to hold.

D'Amato said that if the prisoner load becomes too large because of the stepped up efforts, the overflow might be assigned to nearby federal facilities, with the city paying the $42-per-day cost of keeping each prisoner.