For some time now, perhaps the most frequent topic of hallway discussion on the floors of two buildings in the 1300 block of G Street NW has been "how Marion might go about replacing Jake, when he might do it, who will replace him, and Jake's reaction," according to one senior District of Columbia housing official.

"Jake" is Lorenzo Jacobs Jr., director of the city's Department of housing and Community Development and one of the city's most frequently criticized agency heads during the campaign for mayor that just ended.

Mayor-elect Marion Barry Jr. has said publicly that Jacobs will be the first person removed when Barry takes office. A source familiar with Barry's transition team operation said that not only Jacobs, but others in the top echelon of the city housing department, may be replaced. Housing is the subject of one of the task forces Barry's team is setting up.

Yesterday's numerous housing officials and staffers interviewed in the department's main offices at 1325 and 1341 G St. NW attested to the depth of concern over how the Barry administration may change the housing department. But most said there was no paranoia over possible job losses and no flurry of job resumes hurriedly being typed up.

"People are genuinely concerned, but I haven't seen any mass hysteria," said one top housing official, who added that should he be forced to leave, "I have marketable skills. A lot of people would be interested in my abilities."

"Nobody's sitting around twisting their thumbs and worrying about it," said another senior employee puffing on a pipe in his office. "I feel combortable, but maybe I have a false sense of security."

"Some people (on the staff) may be pleased with the change in administrations, particularly with the change of directorship," said one senior administrator. Jacobs was "too legalistic" and failed to take clear positions, the administrator charged. He predicted that Jacobs would be shifted to another city government post within three months, or would leave the government and set up a private law practice.

Some housing employes complained of uncertainty over whether civil service and city personnel regulations protect their jobs. "It's new to us," said one staff member." . . . We don't know what's going to happen."

Jacobs and his department have come under frequent criticism, with some council members and community workers calling for his resignation.

Two years ago, Jacobs acknowledged that his agency had deliberately made it difficult for city residents to apply for federal rent subsidies, intending to discourage a deluge of applicants. More recently, the U.S. Department of Housing and Urban Development questioned the operation of the District of Columbia's relocation program for displaced families.

Jacobs, a lawyer, insisted during an interview in his ninth floor office yesterday that he has made no plans for his future.

"Nobody's paranoid," Jacobs said. "We're going about business in the usual manner. I assume that at some point I will talk to the new mayor.I don't have any plans. I haven't focused on it."

Jacobs suggested that he thinks Barry has a right to choose his "lieutenants," as he put it.

If his critics compare the period immediately before the housing and community development department was credited in 1975 with its operation since then, said Jacobs, they would see that his department has accomplished much.

Many of his subordinates agreed that they had been attacked unfairly.

"Our problem," said one senior official, "is that we haven't done too good a job selling and telling our story. You can bring in Jesus Christ and set him up here. There is only so much money available. There is only so much you can do."