Prime Minister Menachem Begin today accused the Reagan administration of attempting to undermine his political authority by encouraging internal Israeli dissent over Begin's flat rejection of the president's Middle East peace initiative.

According to an official announcement today from the government press office, the prime minister, in an interview with the Israeli Army magazine, "accused American officials and journalists of interfering in the internal affairs of Israel through leaks to the press, statements by various officials or aiding rival political parties."

The announcement gave no elaboration of these accusations.

The announcement of the Begin interview followed by a few hours warnings by a number of Israeli officials that Begin is serious about his threat to call early national elections next spring and to use the occasion as a national referendum to bury Reagan's Middle East proposals.

Begin's challenge to his political rivals to call early elections has been greeted with widespread skepticism here and seemed to be part of a continuing Israeli government effort to persuade the Reagan administration to abandon its peace proposals.

Israeli officials, saying they sensed that the administration hopes to use the president's initiative to encourage internal Israeli dissent against Begin's policies toward the occupied West Bank and Gaza Strip, seemed particularly anxious to deliver the warning to Washington.

"If there were any transatlantic ideas that by coming up with a new plan you would be able to force a certain change in the government's attitude, it seems that would be counterproductive in that the government is willing to take up the challenge," an official said.

Pointing to public opinion polls that show Begin riding a new crest of popularity, the official said such a strategy by the United States would not only fail, but would "backfire" because the Begin government would use it as "justification to go to the polls and get a new mandate" for its policy to maintain the occupied territories under Israeli control and eventually to absorb them into the country.

In an unusual procedure, the official volunteered these statements at a briefing for foreign correspondents that is normally confined to foreign policy issues. He said the threat of early national elections over the Reagan initiative had foreign policy implications because it was "another indication that this is going to be our position -- nonacceptance of the American proposals."

The prime minister issued the threat yesterday during a debate in the Israeli Knesset (parliament) over the Reagan proposals. Taunting the main opposition Labor Party, he suggested elections be held next May or June and that the main issue be the future of the West Bank and Gaza.

"We'll see who speaks for the majority," Begin said in challenging the Labor Party leadership.

The skepticism that greeted Begin's remarks centered not on the prime minister's desire for early elections but on questions of whether he can maneuver through the intricacies of internal Israeli politics to arrange such an electoral test as early as next spring.

The current Knesset term is due to expire in the fall of 1985. Begin clearly wants elections before then in the belief he can strengthen his grip on the government, but to do so he will need the cooperation of his other government coalition partners.

One of those partners, the National Religious Party, lost half of its seats in the Knesset in the last national elections and is not anxious for new elections until at least a year from now, by which time it hopes to have improved its political position.

Labor Party spokesmen said today they would be happy to take up Begin's challenge if they were convinced that he is serious about it. Despite such statements, there is also skepticism here that the Labor Party, which is divided internally and is losing popular support according to recent public opinion polls, could mount an effective challenge to the Begin government as early as next spring.

If Begin yesterday challenged his Labor Party opponents, today's statements by, among others, Uri Porat, the prime minister's chief spokesman, seemed a direct challenge to Washington that the government will go to the polls to obtain an even stronger mandate for continued Israeli control of the occupied territories.

In making the statements, they may also hope to avoid a real test of their own confident predictions by convincing the Reagan administration to drop its call for a freeze on new Jewish settlements in the West Bank and Gaza and the eventual linking of the territories to Jordan.

There seems little question that if elections were held now Begin's ruling Likud bloc would be returned to power with a possibly historic mandate. Recent public opinion polls show the war in Lebanon and the destruction of the Palestine Liberation Organization forces there have greatly boosted Begin's personal popularity.

But critics of the government note that just prior to the invasion of Lebanon in June Begin appeared to be in political trouble, and they hope that domestic problems -- coupled with a possibly lengthy and costly Israeli occupation of southern Lebanon -- will quickly erode the euphoria that followed the military victories. The Israeli economy remains in serious trouble, as evidenced by the announcement yesterday of a new government plan aimed at reducing the annual inflation rate from 130 percent to 85 percent.

Begin, however, has proved to be a remarkably resilient political leader since he first came to power in 1977. Even his harshest critics agree that dislodging him from power will not be easy, particularly when the alternative is a Labor Party leadership that is generally seen as divided and lackluster.