U.N. Ambassador Jeane J. Kirkpatrick, tacitly conceding that President Reagan did not offer her the kind of job she considers necessary to exert strong conservative influence on the administration, announced yesterday that she is leaving government in order to "speak out clearly" about her views on the proper course of American foreign policy.

After a 35-minute private White House meeting with Reagan, Kirkpatrick ended weeks of speculation about her future. Her conservative supporters had campaigned intensely to persuade the president to carve out an important new role for her in his second term.

Many administration officials believe that retired Lt. Gen. Vernon A. Walters, the State Department's chief diplomatic trouble-shooter, is the leading candidate to succeed Kirkpatrick. But they have cautioned that the choice is not certain.

Well-placed sources within the administration said Reagan made clear to Kirkpatrick in the meeting that she could have a job overseeing U.S. foreign aid activities.

Aware for several days that this would be his offer, Kirkpatrick declined in favor of returning to Georgetown University, where she is a political science professor. Yesterday, she appeared before reporters to read a statement that she said she had written Tuesday night.

It concluded: "I now feel that I can best serve the president and our shared objectives for the United States and the world by returning to teaching and writing. In private life -- perhaps even more than in public life -- I can speak out clearly on behalf of such shared foreign policy objectives as restoring and preserving American strength, supporting democracy and independence in the hemisphere, defending our friends, our principles, and our interests in the Middle East and elsewhere."

Administration sources, familiar with Kirkpatrick's thinking and the internal maneuvering about her future, said her remarks were intended as an acknowledgment and expression of concern about her belief that control of U.S. foreign policy has been captured by Secretary of State George P. Shultz and the administration's moderate wing.

The sources added that her statement also was meant as a warning that she is prepared to criticize administration policy publicly if, in her view, it deviates from her strong beliefs that the United States must maintain a tough line toward leftist activity in Central America and other Third World regions.

According to the sources, Kirkpatrick told Reagan yesterday that some members of his administration do not agree with foreign policy positions on which he twice campaigned successfully for the presidency.

The sources said they did not know whether she specifically mentioned Shultz, but one noted that "the thrust of her remarks was unmistakable." Another added: "She does not regard many of Shultz's ideas as those in which Reagan truly believes."

Kirkpatrick's decision clearly disappointed administration conservatives, one of whom said, "We're losing one member after another of the real Reaganaut team."

The reference was to departure from the top policy-making circle of former national security affairs adviser William P. Clark, who subsequently became interior secretary and announced plans to retire; White House counselor Edwin Meese III, nominated as attorney general, and Faith Ryan Whittlesey, White House public liaision director nominated to return to her former post as ambassador to Switzerland.

Conservatives, who regard Kirkpatrick almost reverentially as a feisty and articulate spokesman for their views, had made a priority of trying to keep her in an administration with such conservatives as Defense Secretary Caspar W. Weinberger and CIA Director William J. Casey.

They are seen as countering moderates headed by Shultz and former White House chief of staff James A. Baker III, confirmed Tuesday as treasury secretary.

In four years at the United Nations, Kirkpatrick was a combative advocate of U.S. interests, frequently irritating Third World and communist bloc delegates with her quick replies to criticism.

Nevertheless, many western diplomats, appraising her tenure yesterday, said she had helped the United States to achieve a stronger position in the world body because her toughness in dealing with Third World delegations had forced them to give grudging but increased cooperation to resolutions of interest to the West.

When Clark left as national security affairs adviser in October 1983, Shultz and Baker turned aside conservative attempts to place Kirkpatrick in Clark's job by persuading Reagan to name Robert C. McFarlane as adviser.

After Reagan's reelection last November, Kirkpatrick, who had announced her intention to leave the United Nations, made clear that she would remain in the administration only in a top-ranking foreign policy post such as that of national security affairs adviser or secretary of state.

Reagan rejected conservatives' arguments that he should switch McFarlane to the White House counselor's job to make room for Kirkpatrick. He announced almost immediately that he planned no changes at the State or Defense departments or in McFarlane's job.

Shultz and Baker, expressing concern about the likelihood that Kirkpatrick might use a powerful vantage point to undermine State Department authority, opposed efforts to relocate her in a major position.

Richard Viguerie, a prominent New Right spokesman, said yesterday: "It's a disappointment that the president wouldn't stand up to George Shultz."

Rep. Jack Kemp (R-N.Y.) said he hopes that Reagan will "find a place for her" if a high-level post becomes vacant.

As one administration source put it, despite Reagan's personal high regard for Kirkpatrick, "the fact is that when the chips were down, the president went with Shultz."

The best position that the president could offer her was the vaguely defined idea of becoming a "foreign aid czar," and sources said even that idea, developed last week as a conciliatory gesture, won grudging approval from Shultz and Baker only because they were convinced that she would reject it.

Kirkpatrick spoke with warmth and gratitude about Reagan yesterday. Asked if she were disappointed, she replied: "No. No, no, no, no, no."

Kirkpatrick said she had given Reagan her resignation, tentatively scheduled for March 1, at a meeting Dec. 11. Sources said Reagan asked her not to make it public then because he did not want a lame-duck U.N. ambassador.