President Carter defended last night the shakeup in his administration as in the "best interest" of the country and said that, despite the threat of a recession, he intends to maintain a "steady course" in economic policy that place the top priority on combating inflation.

In a nationally televised news conference -- his first in almost two months -- the president lashed out at "the oil lobby," predicting that the oil industry will try in the Senate to "rob" $54 billion through amendments to the administration's proposed "windfall profits" tax on the oil companies.

Carter, adopting the posture of self-confidence that has marked his public appearance since his Camp David "domestic summit conference" earlier this month, appealed directly to the American people for help in beating back industry-supported amendments to the "windfall profits" tax in the Senate.

"This is a democracy," he said. "Your voice must be heard."

The president dacked questions on his political plans, but gave the clear impression he intends to seek re-election, saying he will announce his plans later this year. He also belitted a recent suggestion by Sen. Henry M. Jackson (D-Wash.) that he will be denied the Democratic presidential nomination next year by Sen. Edward M. Kennedy (D-Mass.) after Carter falters in the New Hampshire and Massachusetts primaries.

"Three or four years ago I was running for president against Sen. Jackson," Carter said, recalling the 1976 Democratic primaries. "At that time, he predicted that he would be the next president beginning in 1977. His judgement was not very good then, and now I'm ready for the next question."

The news conference was dominated by questions about last week's Cabinet purge and other domestic issues. In response to the only question he received on foreign policy, the president rejected suggestions that the overthrow of the Somoza regime in Nicaragua was engineered by Cuba.

"It's a mistake for Americans to assume or to plan that every time an evolutionary change takes place or even an abrupt change takes place in this hemisphere that somehow it's the result of secret, massive Cuban intervension," he said. "The fact in Nicaragua is the incubent government -- the Somoza regime -- lost the confidence of the Nicaraguan people."

Saying that "the people of Nicaragua have got enough judgement to make their own decision," Carter pledged that the United States "will use our efforts in a proper fashion, without interventionism, to let the Nicaraguans, let their voices be heard in shaping their own affairs."

On economic policy, the president said he planned no special action to combat the continuing decline in the dollar, saying the strength of the dollar will depend on the soundness of the economy and whether the United States comes to terms with its energy shortage. He warned that failure to enact his energy program could weaken the dollar.

Asked about the prospect of a recession, which is being forcast by administration economists, and the rise in unemployment that would bring, Carter replied:

"I think this is a time for stability. I think it's a time for the continuation of the present economic, monetary and budgetary policies."

When he was at Camp David, the president added, there was "almost unanimity" from those he spoke with that "inflation is the biggest single threat to the American people, both rich and poor, and to the future of the nation's economy in the months ahead."

He added:

"There will be a period of slow growth in our country. I believe that next year we'll see this growth restored to a moderate rate . . . We're going to watch unemployment, but my judgement is to maintain our steady course [and] remember that inflation is the biggest threat to all Americans at this time."

In response to other questions, Carter strongly defended his purge of the Cabinet last week, which involved the firing of three secretaries and his acceptance of previously offered resignations from two others.

"I felt and still feel that I had to make some changes in my Cabinet -- to create a new team of work with me, a team that will be united, that will be forceful and aggressive and competent in facing the problems that we must meet in the months ahead.

"I have no apology to make for it," he continued, adding that he had decided the "abrupt action" he took was preferable to "dragging it out."

On specific aspects of the shakeup, the president:

Said that Housing and Urban Development Secretary Patricia Roberts Harris, nominated to succeed ousted Health, Education and Welfare Secretary Joseph A. Califano Jr., has his full support to continue Califano's controversial antismoking campaign and his school desegregation policies. But while affirming support for these policies. Carter refused to say why he fired Califano, saying that's "something I don't care to discuss publicly."

Charged that press accounts of his designation of Hamilton Jordan as White House chief of staff are among "the most grossly distorted of my career in politices." He emphasized that Jordan "will not be the chief of the Cabinet, I will be the chief of the Cabinet," nor, he said, would Jordon seek to dominate Congress. Carter said he named Jordan to the powerful post "because of Hamilton's knowledge of me, his closeness to me, his superb leadership capabilities, the trust that other people in the White House have in him . . ."

The president opened his news conference with a prepared statement that revived the main theme of his address to the nation 10 days ago -- an assertion that "a crisis of the American spirit" can be overcome if the nation unites behind his energy program, beginning with enactment of the "windfall profits" tax on the oil industry.

Describing the tax as critical to the financing of his energy program, Carter predicted that the oil industry will wage "a massive struggle to gut" the tax in the Senate and promised that he will "do everything in my power as president" to win enactment of the measure.

The news conference was Carter's first since May 29 and came after a month of upheaval in the administration, including the president's "domestic summit conference" at Camp David, his July 15 television speech on the nation's crisis of confidence" and his new energy proposals, and his purge of the Cabinet last week.

The news conference, Carter's 51 st as president, also marked the final passage in the stylistic evolution of the president's approach to such sessions with reporters that began with deliberate attempts to contrast the Carter presidency with that of Richard M. Nixon.

Last night's news conference was only the second that Carter has held during prime-time television hours. It was also the first he was held against the ornate backdrop of the East Room of the White House. Previous Carter news conferences have been conducted in the austere auditorium of the Old Executive Office Building adjacent to the White House. CAPTION: Picture, Carter, returning the presidential press conference to prime television time in the ornate East Room of the White House, fields a question from a reporter.

By John McDonnell -- The Washington Post