President-elect Jimmy Carter reached agreement with a key congressional chairman today on the terms of legislation restoring the chief executive's authority to reorganize the government.

Chairman Jack Brooks of the House Government Operations Committee told reporters after a two-hour meeting with Carter that the bill to carry out one of Carter's main campaign pledges should be passed "without much difficulty." The Texas Democrat said his committee will begin work on it as soon as committee assignments have been made.

Thomas B. (Bert) Lance, Carter's choice for director of the Office of Management and Budget, who was in the meeting with Brooks and Carter, said the incoming administration has not yet formulated any specific reorganization plans.

The Legislation Brooks and Carter discussed today would simply give the President authority to submit reorganization plans that would become effective in 60 days unless vetoed by either house of Congress.

Past Presidents have enjoyed that authority for more than 25 years, but Congress let it lapse in 1973 at the height of its dispute with Richard Nixon.

Brookes said the bill he will introduce would give Carter reorganization powers for four years, as he requested. It would also incorporate a provision, recommended by Brooks and Senate Government Operations Committee Chairman Abraham A. Ribicoff (D-Conn.), to allow the President to amend his own reorganization plans within 30 days of submission.

That provision will have the effect of enabling key members of Congress to put pressure on the President to alter his plans in order to satisfy their objections.

Brooks predicted easy sledding for the reorganization authority because "Congress shares (Carter's) deep concern . . . about making government more efficient and economical."

He foresaw opposition from "all the lobbyists in Washington, all the lawyers and all the public relations people. They will jump through hoops when you change the format. They know old Joe won't be standing there with his hand on the switch any more. Joe's going to be down there shoveling."

Brooks noted that the legislation discussion today will not allow Carter to incorporate in a single department all the existing energy agencies, which Brooks called "the most obvious need" in government Carter could reshuffle units within agencies but could not create, merge or abolish whole departments.

Brooks also said it would be "difficult" for Carter to fulfill his campaign pledge to reduce the number of government agencies from 1,900 to 200, but said it was a "good ambitious taget." And, as he has done before, he cautioned against Carter's pledge to institute zero-base budgeting for all government agencies, saying Carter should concentrate first on those with "the fattest" budgets.

Lance, too, indicated he favored a more gradual implementation of zero base budgeting than Carter originally suggested.

The meeting with Lance and Brooks was the main item on Carter's agenda this cold, rainy day. He also visited with two prospective members of his White House staff: Jim King, one-time aide to Sen. Edward M. Kennedy (D-Mass.) who was trip director of the Carter campaign, and Tim Kraft, youthful director of field operations in the campaign.

Both are expected to be offered positions in the area of political and congressional relations.

While Carter was in these meetings, his mother, Lillian Carter, was released from the hospital in nearby Americans after two weeks of treatment for an arthritic condition in her legs. She told reporters she expects to be able toattend the Jan. 20 inaugural.

Carter, in an interview with the Americus Time-Recorder published today, said he thinks "Miss Lillian" will "spend most of her time" in Plains, and will go to the White House to stay with her daughter Amy only "if we were to be away for a while" on a trip.

Carter also told the newspaper he has invited members of his Plains High School graduating class to a reunion in the White House on Jan. 22.