A senior official of Nicaragua's revolutionary regime yesterday denied "categorically" that his government is helping to smuggle arms to leftist guerrillas in El Salvador, and he charged that the United States has launched "a vast plan" of political, economic and military actions against his country

The charges were made at a news conference here by Jaime Wheelock, Nicaraguan minister of agriculture and agrarian reform and a leading member of the Sandinista National Liberation Front, the dominant force in Nicaragua's government.

In a speech later to the Latin American Studies Association at the Shoreham Hotel, Wheelock also put forward what had been billed in advance as "a major Nicaraguan proposal" for peace in Central America.

However, it turned out to be a reiteration of the plan adopted at a recent meeting in Nicaragua of the Permanent Conference of Political Parties in Latin America (COPPAL).

COPPAL is a grouping of Latin American Social Democrat and other left-of-center parties.

Its Managua program, reprinted in a full-page advertisement in The Washington Post on Feb. 24, calls for resolving the Salvadoran conflict through negotiations between the civilian-military government and the rebels, and for the United States to end "its declared policy of intervention" on behalf of the government.

That idea has been rejected repeatedly by the Salvadoran government and the Reagan administration. As a result, it seems unlikely that Wheelock's proposal offers any chance for resolving the growing tensions between the United States and Nicaragua.

In fact, during his news conference Wheelock seemed primarily intent on reciting an almost nonstop litany of charges that the United States is trying to overthrow the Sandinista government and working to "facilitate a fascistic solution and further militarization" in Central America. Asked for proof of U.S. activities aimed at destabilizing Nicaragua, he charged that anti-Sandinista groups in Nicaragua and in neighboring countries such as Honduras are controlled and financed by the Central Intelligence Agency. He asserted further that these operations are directed by Nestor Sanchez, an anti-Castro Cuban exile who reportedly was among the leaders of the unsuccessful 1961 Bay of Pigs operation. In addition, Wheelock charged that Thomas O. Enders, assistant secretary of state for inter-American affairs, had told a closed congressional hearing that $19 million had been committed to a destabilization program aimed at Nicaragua.

Wheelock also implied strongly that the United States has incited the Nicaraguan newspaper La Prensa and various trade unions in his country to criticize the government "to sabotage our economy and turn the people against their own revolution."

"There are too many things happening at once to be a coincidence," he said. "All these elements lead to one conclusion. The CIA is the only force with the power to do these things at once. It's difficult to prove it specifically, but the tracks are there."

The Washington Post has quoted informed sources as saying that President Reagan had approved a proposal to support foreign governments in political and paramilitary operations against Cuban-Sandinista activities in Central America and that the National Security Council was considering a $19 million proposal to back these activities.