President Carter yesterday stepped up the defense of the budget proposals he will make to Congress on Monday, asserting that they will meet many of his anti-inflation goals but not at the expense of "disadvantaged Americans, poor Americans or those who are unemployed."

The president told a nationally televised news conference that in the budget he will exceed his goal of reducing the federal deficit to $30 billion but will increase spending for the poor by $4.5 billion and set aside $11 billion for jobs programs and job training.

"This budget, when it is examined in its entirety... I think will be seen by any fair person as meeting the legitimate needs of those who are most dependent on government, on meeting the defense needs of our country, on being well balanced, on being fair and contributing greatly to controlling inflation," he said.

The news conference, Carter's first since Dec. 12, came five days before his budget for the fiscal year that begins Oct. 1 will be sent to Capitol Hill, where it is expected to set off a protracted and at times bitter dispute between the president and liberal members of his own party over cuts in social welfare programs and a proposed increase in military spending.

Seizing the opportunity presented by the news conference, Carter read a prepared statement defending the budget before the expected onslaught of criticism next week.

In response to questions on another key domestic topic -- energy prices -- the president clearly sided with Energy Secretary James R. Schlesinger in an internal administration debate over whether to move quickly to import natural gas from Mexico.

Schlesinger has argued that the United States must place first priority on developing its own resources, including gas fields in Alaska, a line Carter took yesterday.

"In the future, the next few months, there is no urgency about acquiring Mexican natural gas," he said. "We have at this moment a surplus of natural gas in our own country and the statements made by the secretary of energy were related to that fact."

When he visits Mexican President Jose Lopez Portillo next month, the president added, "I am not going down there to negotiate the price of natural gas."

Asked about domestic oil prices, Carter said they will have to be "raised substantially," leaving open the possibility that he will act to achieve that purpose this year. But he said no decisions have been made on that issue and he conceded that his desire to increase oil prices to encourage conservation and his goal of controlling inflation "work against one another."

Carter failed last year to persuade Congress to enact legislation raising domestic oil prices through imposition of a tax on production. He has made commitments to U.S. allies that the price of American oil will rise to world levels by the end of 1980.

On other topics during the news conference the president:

Defended his firing of Bella Abzug as co-chairwoman of the National Advisory Committee for Women and said he had "no aversion" to the kind of public criticism Abzug and the committee had leveled at him. Noting that he had selected Abzug for the post, he said, "It didn't work out. The committee has never been well organized. Their functions have never been clearly expressed to me."

Called his invitation to former president Nixon to attend the White House state dinner honoring Chinese Vice Premier Teng Hsiao-ping Jan. 29 "a fair thing and a proper thing." Despite the Watergate scandal, Carter noted, "one of the major achievements of President Nimon was to open up an avenue of communications and consultation and negotiation with the Chinese which resulted ultimately in normal relationships." He added that Teng had asked to meet with Nixon while in the United States.

Said he will continue to support federal price supports for tobacco despite increase federal warnings about the health hazards of smoking. He said one result of those warnings, which he also supports, is that smokers "now have safe cigarettes to smoke, with less nicotine and less tar."

The president was critical of, but careful not to reject outright, a proposal by one of his main Democratic Party rivals, California Gov. Edmund G. (Jerry) Brown Jr., on how to deal with the sensitive issue of inflation and government spending.

Brown last week proposed adoption of a constitutional amendment to require a balanced federal budget and said the states should pass resolutions to convene a constitutional convention to achieve that goal if Congress fails to do it.

Carter said a constitutional convention "would be extremely dangerous" because it could result in a "radical departure" from the existing constitution.

But the president was careful in dealing with Brown's suggestion of a constitutional amendment to force a balanced budget. He said devising such an amendment would be "a difficult matter" because of the need to provide for "unanticipated military or security needs" or to bring the economy out of a depression.

"So I think this is something that ought to be approached very gingerly, very carefully, and if there is any constitutional amendment, it ought to be done in accordance with practices that we have used in the past," he said.

On the subject of his own budget proposals, Carter said the deficit will be about $29 billion. He said it will also meet his goal -- one year early -- of reducing federal spending to 21 percent of the gross national product (the value of all goods and services produced in the country).

For the current fiscal year, the federal deficit amounts to less than 2 percent of the gross national product. In the next fiscal year, the president said, that figure will be reduced to 1.2 percent of GNP. Based on the figures Carter supplied, it appeared the government is projecting a GNP of about $2.417 trillion for fiscal year 1980.