Senate Democratic Whip Alan Cranston (D-Calif.), an ex-newspaperman, ruefully told reporters yesterday that he is resigning his role as Capitol Hill's unofficial reporter on congressional leadership meetings with President Carter.

Ever since he was elected whip Jan. 4, Cranston has been attending bi-weekly Tuesday morning leadership breakfasts with Carter - and then coming back and telling the press "on the record" at his ow news conference many details of what Carter and congressional leaders said to each other.

Cranston said yesterday that he isn't going to do it anymore because "some of the stories [that subsequently appeared in the newspapers] might not have improved my relations with people."

He denied that anyone had put any pressure on him to close down his experiment in open government, but conceded that several persons had spoken to him about some of the things he had revealed. He wouldn't identify them.

However, reporters who cover the House noted that Speaker Thomas P. (Tip) O'Neil Jr. (D-Mass.) had once or twice in recent months made needling references to the fact that Cranston was speaking openly about what went on at White House meetings.

Cranston's briefings were particularly valuable to reporters, because there is seldom any official briefing from the White House or anyone else on what goes on at the leadership meetings.

At least three of his briefings got him in some hot water.

One involved his report that Carter, in brushing aside fears about Soviet reactions to some of the things Carter said, had remarked sarcastically, "Some people get upset every time Brezhnev sneezes." Cranston decided after that one that the report might have done some damage to U.S.-Soviet relations and announced he wouldn't quote Carter directly anymore, only paraphrase.

Another story that caused some upset was his report that Vice President Mondale had lashed into former President Ford for criticizing Carter. Some reporters who were present got the impression from Cranston that Mondale had said that Ford was worse than Nixon, although other sa say Cranston didn't say that. At any rate, the whole story caused more rumpus than Cranston expected.

Yesterday, Cranston said his report on last week's discussion of economic policy at the White House had been misinterpreted.

"The general impression from the last one was that there was more conflict between congressional leaders and the President over the budget," than was actually the case, Cranston said. He was referring to stories saying Cranston had told reporters he and other congressional leaders confronted the President and warned him severely that he shouldn't subordinate domestic programs for the poor and working man to the goal of balancing the budget. "The stories that came out have not been particularly helpful," he said.

Cranston said, "I got into the role of being a Jody Powell pool reporter" on private meetings between the leaders and the President. (Jody Powell is the President's Press Secretary.)

Cranston, who was a reporter for the old International News Service in Europe and Africa in 1937-38, said he didn't tape the meetings or take complete notes and he had started to feel uncomfortable quoting other people. Hencerforth, he said, he felt he should leave it to others to tel reporters what they had said at the meetings if they chose.

Crantons said he won't stop holding press conferences, but he simply won't hold them right after the biweekly meetings with Carter, but perhaps several days later in the week.

Someone asked what difference that would make. Cranston laughed and said it would give him more time to think about how much he should say and to see "who leaked what" in the meantime.