THIS WEEK, Jeane J. Kirkpatrick is retiring from her post as U.S. ambassador to the United Nations and changing allegiance from the Democrats to the Republicans. Last week, Kirkpatrick gave some reasons behind her shift of party and discussed future plans:

"I'm becoming a Republican," she said, "because finally I began to feel it was perfectly clear that I wasn't thinking like a Democrat. I wasn't acting like a Democrat. I didn't feel like a Democrat any more. The people with whom I found I could work most closely on issues I cared about were almost always Republicans.

"I don't agree with everything about the Republican Party, but I realize there are more people called Republicans working toward ends that are important to me than people called Democrats. I believe that our answers to foreign policy and defense problems will determine our security and that of our friends in Western Europe, Israel and elsewhere. That sounds melodramatic, but I think we live in one of those periods when the questions are ultimate and the risks are terrible."

The foreign policy of the Democratic Party, she said, represents dangerous appeasement. "To an unusual extent, the world is balanced on a razor's edge. The policies of the next five years can determine whether whole continents fall apart and how safe or unsafe we, the democracies, become. So many countries could go either way."

Kirkpatrick traced her disenchantment with the Democratic Party from the late '60s to today. She cited New York Gov. Mario M. Cuomo's keynote speech to the last Democratic Convention as an example of what's wrong with the Democratic Party: "At the rhetorical level it was a brilliant speech, but one might have thought one was in a Depression bread line. You couldn't tell whether you were in 1984 or 1932."

In the '60s, Kirkpatrick recalled, "There developed in the Democratic Party a strong undercurrent of counterculture which was incompatible with the tradition of Democratic mainstream views." The emerging Democrats, Kirkpatrick said, perceived America "as a sick society, our history as a dismal failure -- dead Indians, scheming white settlers, the rape of the environment. We were, in short, a corrupt society, which had gotten into a terrible war because we were terrible people."

A struggle took place for the soul of the party between the middle and the emerging "new left." After George McGovern's landslide defeat in 1972, Kirkpatrick and others from what she calls "the mainstream of the party" -- those affirming pro-growth, anti-communist views -- founded the Coalition for a Democratic Majority.

The CDM group, Kirkpatrick said, was soon labeled "neo-conservative," a label she laughed at. "Nobody had ever called us conservatives until then. Under the challenge of the new left, I guess we looked conservative."

In 1976 she voted for Gerald R. Ford -- "I never said that before" -- she didn't tell anyone because she wanted to preserve her identity as a Democrat. "I thought Ford was a man of judgment, moderation and responsibility, who could make our government work," Kirkpatrick said. Jimmy Carter, she feared, was "too much of a risk because of his lack of national experience."

Her fears, she said, proved more than justified. Indeed, she calls Carter's foreign policy "dangerous, romantic and naive," singling out for special disapproval "the neglect of our military strength." She also called the Carter administration "an unreliable friend to Israel."

A turning point in her Democratic disaffection came when under Ford, a Democratic Congress refused to vote U.S. assistance to the non- Marxist forces in Angola. "I was absolutely dismayed by this, I still am." She likens this vote to the present congressional refusal to finance the contras battling the Sandinista regime in Nicaragua.

In April 1980, Kirkpatrick first met Ronald Reagan, "and I liked him." After doing some research, Kirkpatrick chose Reagan over Carter: "It was the first time I had ever broken ranks publicly with the Democratic Party."

Earlier, in 1979, Kirkpatrick had written an article expressing doubts about whether the Republicans had spelled out "an inclusive vision of the public good." But "the Republicans do better today" in articulating such a vision, she said, "and I have also changed my views on some of these issues.

"I think the Democratic Party mainstream reflected the answer to the problems of the Depression, and I think those answers were good answers -- that it was important to provide the kind of central security net, minimum protections for everyone in a highly industrialized urbanized society."

For the '80s, she argued, "the Republican Party has better answers to the problems -- with deregulation and dismantling of unnecessary restraints on the economy and the restoration of American strength in foreign policy." Government growth, she said, once a legitimate response to problems of the Depression, had by 1980 become a problem: "The government was consuming too much of our total product, stifling too many of our creative energies and innovative capacities.

"I do not believe the Republican Party has removed the safety nets," Kirkpatrick said. "I don't think they have attempted to dismantle the humane foundations of a decent society. I don't think they have made a frontal assault on the welfare state.

"If I believed they had, then I could not become a Republican because I believe very deeply in the basic protections of the welfare state, just as I believe deeply in the civil rights revolution and I believe in affirmative action, Social Security, Medicare and the basic protections which we s an affluent society can afford to provide American citizens."

In the world today, Kirkpatrick sees two major struggles: The East-West struggle, which she believes the United States is meeting through military buildup, and the struggle for the Third World. She believes the Third World struggle is as important as that between East and West, but she doesn't want to see U.S. armed forces involved: "I think we should be very cautious about the use of American force but be ready and willing to help other countries help themselves."

The new Republican doesn't endorse everything the administration does, however. In the case of Lebanon, for instance: "I don't think anybody would say our Lebanon policy was very successful. I think once the Israelis had gone into Lebanon and the Syrians and PLO were on the run, we should not have discouraged the Israelis from running the Syrians out of the Bekaa (Valley) and the Palestinians out of Beirut."

And what of her future? Would she consider elective office? "If I thought I could make a big difference to major problems, then I suppose I would feel I had to try," she said.