President Reagan said yesterday that his proposed 10 percent increase in defense spending next year is the "absolute minimum" necessary and that he cannot accept the smaller increases approved by the House and contemplated by his Senate Republican allies.

He hinted at some future "flexibility," but said it would not extend to the 6 or 7 percent increase suggested as a possible middle ground by some Republicans on the Senate Budget Committee.

"I'm going to fight as hard as I can for what we've proposed in the line of a defense buildup," Reagan told six White House correspondents in an Oval Office interview.

"We could not go back down to those figures without reducing our readiness, reducing even the size of our military, number of men, and without eliminating and cutting back on weapons systems that I believe are necessary."

Reagan's proposed $239 billion Pentagon budget for fiscal 1984--a 10 percent increase after inflation--would be held to a 4 percent increase under a budget resolution passed by the Democratic-controlled House last week. Senate Budget Committee Chairman Pete V. Domenici (R-N.M.) delayed a Senate vote after Reagan promised to show some "flexibility" on defense spending.

But White House officials said yesterday that Reagan, now waging a full-scale lobbying and public relations offensive for his rearmament plans, intended to signal a hardening line against compromise before the Senate vote. That is standard Reagan negotiating strategy--taking a hard line until the last possible minute.

In the interview, Reagan also:

* Disagreed with those who believe the recent sharp exchanges between Moscow and Washington signal a return to the Cold War attitudes of the 1950s. "I don't think there was anything particularly new in the rhetoric that was used by Soviet leader Yuri V. Andropov and has been used by other Russian leaders before him," Reagan said.

* Disclosed that the Soviet Union has rejected U.S. proposals to tighten the verification procedures in two treaties limiting nuclear weapons tests. A White House official said later the Soviet rejection came Monday.

* Dodged questions about possible U.S. involvement with Honduras-based insurgents seeking to overthrow the Sandinist government in Nicaragua. While the issue has been raised by U.S. allies in the U.N. Security Council, Reagan said it was an intelligence matter and he would not discuss it. Instead, he offered a defense of administration actions in neighboring El Salvador.

Reagan was interviewed by reporters Tom DeFrank of Newsweek, Susan Page of Newsday, Gary Schuster of The Detroit News, Benjamin Taylor of The Boston Globe, Paul West of The Dallas Times-Herald and Loye Miller of Newhouse Newspapers.

On defense spending, Reagan was questioned about a letter he sent this month to Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) suggesting that, while he wasn't making any promises, he might find some "flexibility" when the Senate returns after Easter. Reagan was also asked whether he would settle for an eventual House-Senate compromise of 5 or 6 percent.

"I think it would be violating what the government is intended to do," he said. "The one prime responsibility of government is to protect the lives and freedom of its citizens. The budget we submitted and the budget figure we believed was the absolute minimum that was necessary to continue redressing our defensive capability, which had been allowed to deteriorate so badly in the previous decade."

Reagan said his comment about "flexibility" did not extend "to the extent they're suggesting changing" his defense budget. He said he was not ready to detail any concessions and would not do so until the Senate returns. "I was very careful not to make a promise," he said.

Reagan would not disclose the details of the new U.S. proposal, presented to the Soviets at the Geneva arms talks yesterday, for an interim agreement on reduction of intermediate-range nuclear weapons in Europe. He will unveil it publicly before a group of NATO ambassadors at the White House today. The president said yesterday that "there has been no change in my position or ultimate goal" to eliminate all intermediate-range missiles in Europe.

Asked whether he believes an arms control agreement is "realistic" in light of the recent harsh exchanges with Andropov, Reagan replied "yes," and went on to dismiss the Soviet leader's harsh rhetoric of last weekend.

"In the United States we have to be used to being called 'imperialists' and several other things and charges made that we're trying to seek some advantage . . . , " Reagan said. "I don't think there's really been any escalation of that at all."

The president complained that some editorials in American newspapers were "quite irresponsible" in criticizing his call last week for long-range studies into a futuristic anti-ballistic missile defense system. He said the proposal was not a "smokescreen" to avoid discussion of the arms race, and described it as a realistic idea.

He expressed uncertainty about what the high-technology research might produce, but said an American president might "offer to give that same defensive weapon" to the Soviets "to prove to them that there was no longer any need for keeping these missiles."

Asked whether Interior Secretary James G. Watt had become a political liability, Reagan blamed Watt's critics for what he said is an "absolutely false" public view of the administration's environmental record. Reagan said the administration is "spending more money on parks and on acquisition of parks . . . than the previous administration had spent in all its four years." The White House said later, in response to queries, that Reagan was in error on that point.

Voicing an opinion that President Carter also held, Reagan said he thinks the four-year presidential term is too short. "You really can't in four years carry through programs that may be necessary," he said. But he added that he wasn't providing a "tipoff" as to whether he will seek another term.