The military exercises that will be staged by the United States and Honduras along the borders and coasts of Nicaragua for the next five months are part of a newly devised long-range Reagan administration plan to prevent the spread of leftist regimes in Central America, administration officials said yesterday.

These officials said the plan, hammered out during the past four weeks in interagency discussions initiated by President Reagan and his national security advisers, includes additional U.S. support for a growing number of guerrillas opposing the leftist Sandinista government of Nicaragua and the supply of arms by Israel to U.S.-backed governments in Central America.

The creation of the Kissinger commission to devise a policy of increased U.S. aid to Central America and a stepped-up White House campaign to convince Americans that they are threatened by the Soviet and Cuban presence in the region also are part of this plan, the officials said.

"What we've got is a consistent Reagan policy to stabilize the situation in El Salvador and not have that country and others in the region go communist," one official said. "It is a policy aimed at . . . preventing the spread of the Cuban syndrome on the Central American mainland."

Reagan yesterday kept up rhetorical pressure on the Sandinistas in Nicaragua at a short question-and-answer session in the White House briefing room. Leaving open the possibility of a naval blockade against Nicaragua, he said it would be "extremely difficult" for a satisfactory peace settlement to be reached in the region as long as the Sandinistas remained in power.

Reagan said it was the Sandinistas and not the U.S.-supported "contras" opposing them who are violating international law. In a remark later disputed by officials of the Organization of American States, he said that "the Sandinista government is in violation, literally, of a contract that they made with the Organization of American States" to guarantee democratic freedoms in Nicaragua after the dictatorial Somoza regime was overthrown in 1979.

An administration official said after the president's remarks that he realized that "Nicaragua and Cuba and the Soviets must have some doubts about our intentions at this point."

This official denied that the administration has embarked on a campaign to overthrow the Sandinista government, but said that these doubts were being deliberately raised in an effort to persuade the Sandinistas to reduce their support of leftist rebels in El Salvador. The official declined to speculate on what the United States would do if Nicaragua continues to aid the insurgents.

"Everything that we're doing for the purposes of a military exercise," another official said, "we'd also be doing if the aim were to overthrow the Nicaraguan government."

This point was made in detail by Adolfo Calero, a member of the ruling council of the U.S.-supported guerrillas opposing the Sandinistas in Nicaragua. Calero said the extended presence of a large U.S. military force in the region would provide a "shield" for a stepped-up guerrilla military campaign this autumn.

He called the increased U.S. military presence "more moral support" and said it could "prevent Cuban intervention" to aid the Sandinistas and "stop the Sandinistas from going into Honduras" in pursuit of contras seeking sanctuary. "There is a stage being set up," Calero said, for some "spectacular" moves by the anti-Sandinista guerrillas.

"Everything adds up to the downfall of the Sandinista government," Calero said in an interview. "It has to happen, if not by the end of this year, than by the beginning of next year."

However, a senior Reagan administration official said that U.S. assessments of the contras' military strength did not support this assessment. He said their various military groups totaled about 12,000 fighters, compared with 25,000 Nicaraguan troops plus 50,000 in militia forces.

This official said the 2,000 U.S.-trained guerrillas in the core group were good troops but that many of the others were "ralliers" who had joined the insurgents because of their strong anti-Sandinista feelings and lacked military experience.

The U.S. official confirmed that the Reagan administration intends to continue its support and supply of these rebels, unless forbidden to do so by Congress, but that their chief value would be to "harass and pressure" the Sandinista government in Nicaragua.

Meanwhile, Pentagon officials said the joint military exercises the United States will conduct with neighboring Honduras, from which some of the anti-Sandinista guerrillas operate, would last through January.

The U.S. aircraft carrier Ranger and its accompanying warships are off the Central American coast, and the carrier Coral Sea and its battle group, now in the Mediterranean, are expected to reach the Caribbean in mid-August. The battleship New Jersey, now in Southeast Asia, is to reach the Pacific coast of Central America near the end of the month.

Gen. John W. Vessey Jr., chairman of the Joint Chiefs of Staff, is about to leave for South America and will stop in Honduras and Panama on the way back. During his stopover he is expected to discuss final plans for the joint exercises with Honduran military leaders.

One administration official said the military exercises will provide "a holding action" while the newly named National Bipartisan Commission on Central America headed by Henry A. Kissinger prepares a wide-ranging report on the economic and security needs of the region.

The Washington Post reported yesterday that the Office of Management and Budget already is preparing proposals for an increase of $300 million in economic aid for the region and $100 million in military aid in anticipation of the Kissinger commission's recommendations.

Reagan said at his question-and-answer session yesterday that "I don't think any such figure has been advanced by us as yet."

Administration officials said afterward that they didn't want to discuss future budget increases now because such talk could interfere with pending budget requests for military aid that have been cut in half by Congress.

These officials also said that the budget proposals, which originated in the National Security Council and are said to have Defense Department backing, have encountered some opposition from the State Department and the budget office.

But the amount of military aid being provided to U.S. allies in Central America is far greater than the federal budget reflects. The costs of the military exercises in Honduras and the Carribean will not be included in any of the totals for military assistance to Central America and do not require congressional approval.

Administration officials also confirmed a New York Times report that Israel has agreed to send to Honduras arms captured from the Palestine Liberation Organization in Lebanon. The Reagan administration has emphasized a "PLO connection" to Nicaragua as part of an intensified campaign to build American public support for the president's Central American policy.

On Wednesday at the White House, Reagan met with a group of Jewish leaders who were told by administration officials that the Sandinistas had driven Nicaragua's small Jewish community into exile.

Rabbi Morton Rosenthal, an official of the Anti-Defamation League of B'nai B'rith, told reporters that Nicaragua had no prior history of anti-Semitism and linked the new attitude to "solidarity" between the PLO and the Sandinistas.

It was the ninth consecutive weekly White House meeting in which Reagan and other officials tried to rally a particular constituency behind the administration's policy in Central America. Faith Whittlesey, the White House director of public liaison, said future meetings would focus on what the Nicaraguan government has done to suppress Roman Catholics and Protestants.

The plan for a concerted campaign to put pressure on the Nicaraguan government while trying to convince Americans that Central America is vital to U.S. strategic interests was conceived by an interagency group that has held a series of meetings starting early in the summer.

Much of the original impetus for the meetings, one official said, came from military and intelligence estimates in late spring indicating that the U.S.-backed government in El Salvador faced extreme military pressure from leftist insurgents and resulting severe internal strains.

The military situation in El Salvador has since improved, the official said, but the meetings continued and produced the plan for increased U.S. involvement in the region.

This official, with whom others agreed, said the increased involvement would have to focus on the basic causes of poverty and instability in Central America, as well as the military conflict. The official said this was the reason Kissinger had been named to head what he called "a high-visibility commission" that is expected to command broad public attention.

Officials said White House national security affairs adviser William P. Clark, his deputy, Robert C. McFarlane, and U.N. Ambassador Jeane J. Kirkpatrick took a leading role in the early discussions. They said representatives of the CIA, the Joint Chiefs of Staff and the State Department also played an important role.

The Joint Chiefs were particularly influential, one official said, because they reflected a growing view within the military that the United States should either devote more resources to Central America or negotiate its withdrawal. "More than anyone, the military doesn't want another Vietnam," an official said.

Kissinger, once scorned by Reagan as a defeatist who wanted the United States to be "second best," is being counted on as a key figure in helping carrying out the new plan, officials said. Within the White House, there is a belief that Kissinger is likely to frame the issue in terms of East-West relations and try to deal with regional questions as part of overall negotiations with the Soviets.

But in a speech Wednesday to the Bay Area Council in San Francisco, Kissinger said that the Soviets are not solely responsible for creating political unrest in Central America.

"Nobody should believe that every problem everywhere in the world is caused solely, or maybe even principally, by the Soviet Union," Kissinger said. "In many parts of the world, especially in the underdeveloped parts of the world, there are indigenous injustices. There is a need for reform that has produced social and political tensions. We shouldn't pretend that the Soviets can solve those problems for us."