Drew Days, an attorney with the NAACP Legal Defense Fund, is Attorney General Griffin B. Bell's first choice to head the Justice Department's Civil Rights Division, informed sources said yesterday.

The sources said that Bell, who was sworn in yesterday morning with President Carter looking on, was expected to offer the assistant attorney general post to Days later in the day.

Bell's selection of Days, who is black, appeared to represent a move by the new Attorney General to assure black groups of his commitment to vigorous civil rights enforcement. He already has said that he intends to name Wade H. McCree Jr. a black and a judge of the Sixth U.S. Circuit Court of Appeals, to the job of solicitor general, the Justice Department's third ranking post.

Bell's nomination had encountered heavy opposition from civil rights groups that charged him with hostility to desgregation when he was an Attlanta lawyer and a federal appeals court judge. Because of this oppostion, 21 senators voted against confirming him.

As Bell moved to fill other key slots at the Justice Department, informed sources said that the front-running candidates for duputy attorney general, the second-ranking job, appeared to be U.S. District Court Judge Frank M. Johnson Jr., of Montgomery, Ala., and Louis F. Oberdorfer, a Washington lawyer and Kennedy-era official of the Justice Department.

The Carter administration is know to have offered Johnson the directorship of the FBI. However, he turned the job down, reportedly because a witch from the judiciary to the executive branch would drastically curtail his pension rights.

But, the sources said, Carter and Bell still hoped that Johnson, 58, could be enticed into the administration by the offer of the deputy's slot. If Johnson stands firm in his refusal to move, the sources added, they believe that the post will go to Oberdorfer.

Oberdorfer, 58, currently is with the Washington law firm of Wilmer, Cutler and Pickering. He served as assistant attorney general in charge of the tax division under President Kennedy in the 1960s.

Erlier yesterday, Bell took the oath of office from Chief Justice Warren E. Burger in a ceremony that included the symbolic opening of the long-locked front door of the Justice Department on Pennsylvania Avenue. The massive steel doors had been locked since 1970 as a security precaution against demonstrators and terrorists.

"We take great pleasure in opening them," Bell told the 700 dignitaries and departments employees at the ceremony. "We 're coming out from behind the barricades. We don't intend to operate behind closed doors."

In introducing Bell, Carter took up the same theme, saying the locked doors had been "symbolic of a separation of the disaffected and disadvantaged from the core of Justice."

These doors will be kept open from now on," the President said.

Afterward, Carter, Bell and Burger toured the Justice Department's Civil Division, which was headed by Burger in the 1950s before his appointment to the judiciary.

In a conversation with Irving Jaffee, acting assistant attorney general in charge of the Civil Division, Carter said that he intends to "move very strongly to put the selection of U.S. attorneys on a merit basis" rather than the political patronage system that now governs their choice.