Mayor Marion Barry said yesterday that the city would undertake the immediate design and construction of a new prison in the District as soon as the city selects a location from a list of federally owned sites to be submitted by the Justice Department.

Barry, speaking after a 90-minute meeting with federal officials over the city's prison crowding crisis, also said Deputy Attorney General D. Lowell Jensen agreed to reconsider the recent cancellation of an agreement allowing city prisoners to be sent to federal institutions if a court-ordered population limit at the D.C. Jail is in danger of being violated.

Justice Department sources said, however, it was unlikely that the federal government would reactivate the agreement, which ended two days ago.

And U.S. Attorney Joseph E. diGenova, who attended the 9:30 a.m. meeting at the District Building, disputed the suggestion that progress on new prison construction is dependent upon the District receiving a list of sites from the federal government.

"The federal government has given the District proposed sites on federal property in the District, and we gave them some sites today," diGenova said at a news conference later.

DiGenova, calling the selection of a jail site a "political imperative," said that the federal government had "talked sites inside the city a number of times. Everybody knows what they are."

Two of the most frequently mentioned possibilities are the old D.C. Jail site, now a vacant lot next to D.C. General Hospital, and St. Elizabeths Hospital, both in Southeast. A draft minority report of a 15-member commission appointed to study the prison issue has also identified as potential sites four military bases in the city, three of which are east of the Anacostia River.

City officials requested yesterday's meeting because of the Justice Department's cancellation of the 4 1/2-month-old agreement under which newly sentenced city prisoners were placed in federal institutions.

The agreement, instrumental in the District's ability to comply with the population limit at the D.C. Jail, allowed about 1,600 prisoners to be sent to federal institutions instead of to the jail or to Lorton Reformatory.

Barry's comments, repeating a pledge he made last spring to construct a new prison in the District, were apparently in response to a Jan. 13 letter from Jensen announcing the government's decision to end the inmate-transfer agreement. That decision, according to sources in the federal govenment, was prompted by the city's delay in planning and building a new prison in the District, a delay caused by the politically sensitive issue of where to build it.

After the meeting, Barry said that Justice was "going to move quickly" to select about 10 possible sites, adding, "We are going to build a new prison in the District of Columbia as soon as we get the site" recommendations and finish designing a facility.

A federal official familiar with the situation, who did not want to be quoted by name, said that Justice hopes to submit its proposals to the city today, but that it is unlikely 10 sites will be proposed.

It is likely that the Justice Department's final recommendation will be the old D.C. Jail site, the source said. Federal officials were researching the land titles to the D.C. Armory and the old D.C. Jail site last night and had reached the preliminary conclusion that they are situated on a single tract of land owned by the federal government, the source said.

D.C. City Administrator Thomas Downs said the city had explained to federal officials that the old D.C. Jail site already had been selected as a construction site for a new wing of D.C. General Hospital. Downs said that the site and funding for the wing had been approved and that the construction designs were almost complete. A hospital official said construction was expected to begin in six to eight months.

Barry, at his news conference, said that he told federal officials it is the city's position that the attorney general is responsible for housing city prisoners. Jensen and the others "tried desperately to make it [the responsibility] mine, but I wouldn't let them," he said.

Barry said the city will remain in close contact with Justice, and as the inmate population at the jail approaches the limit, "we'll talk about their taking additional prisoners."

Federal officials did not address the issue of reactivating the inmate transfer program in such optimistic terms yesterday. "Jensen did not agree to anything other than to listen to them whenever they have a problem," one official said.

By order of a U.S. district court judge, the jail is not allowed to house more than 1,694 inmates, and corrections officials said that 1,525 prisoners were housed there yesterday.

Barry declined to discuss an investigation, reported Thursday in The Washington Post, into allegations that jail Administrator William Long told an officer at the jail to change the official Dec. 7 inmate count because it was over the court-ordered limit.

"Everyone knows that we've had no problems with numbers in the past," Barry said. U.S. District Judge William B. Bryant, who ordered the population ceiling at the jail, has scheduled a hearing on the matter for today.

About 80 inmates are sent to the D.C. Jail each day, most of whom are held there while awaiting trial. Depending on inmate transfers to the District-run facilities at Lorton Reformatory, the number of inmates released and other variables, Downs said, "it could be as short as next week or as long as next month" before the population reaches the cap.

The District is studying the construction of modular housing units at Lorton as an interim step to relieve overcrowding until a new prison is built, which is expected to take at least three years.

Barry indicated, however, that the modular housing being studied, a 400-bed unit, may be permanent, noting, "if you add 400 units down there, that means you can have a smaller prison here" in the city.

Money for the modular facility is to come from $30 million approved by Congress for the construction of a new prison in the District. Though the original bill that allocated the money prohibited the funds to be used for expansion at Lorton, new language was added to the bill in December at the District goverment's request that allows the city to spend the $10 million appropriated this year for "emergency" relief, providing it is repaid, according to Downs, who yesterday repeated that the Lorton modular units would be only temporary.

Last night, the D.C. prison study commission voted to recommend against building a new prison for District inmates, and in favor of funding halfway houses, a drug detoxification center and other programs to cope with the city's criminals.

The majority of the 15-member commission debated for three hours, much as it had for the past six months, with a minority of four supporting a new prison. The minority report will be attached to the majority report sent to the mayor and city council, but it was unclear from last night's meeting which commission members will sign the minority position.

A minority report said its first choice for a construction site would be on the grounds of Lorton Reformatory, and listed five other sites in the District as second choices. Staff writers Karlyn Barker, Sandra Evans and John Mintz contributed to this report.