House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), approaching a legislative showdown on undercover U.S. aid to anti-government guerrillas in Nicaragua, charged yesterday that the Reagan administration has mounted "an unneeded show of strength" in Central America essentially for domestic political reasons.

"I think it's awful, absolutely awful," O'Neill said of large-scale U.S. military exercises planned for the area and a major step-up in U.S. covert assistance to Nicaraguan guerrillas reportedly under consideration.

O'Neill told reporters he thinks administration efforts in Central America are aimed at the 1984 campaign. He did not elaborate.

With 103 amendments filed to the Democratic-sponsored bill to ban further U.S. undercover aid to Nicaraguan rebels, O'Neill expressed concern that the "the same people who opposed the nuclear freeze" will undertake similar dilatory tactics on the Central American measure, including "every type of amendment" and frequent, time-consuming quorum calls.

Rep. C.W. Bill Young (R-Fla.), floor leader for the bill, said there is no basis for O'Neill's concern about time-consuming tactics because the House has agreed to limit consideration of all amendments to 12 hours.

The House, which held a rare secret session last Tuesday to discuss the measure, had been scheduled to begin its public debate this afternoon. But a variety of legislative complications is likely to delay the start of the debate at least until Wednesday, House sources said last night. Among the crucial factors is an incomplete nose-count of where House members stand on the issues under consideration.

The vast majority of the amendments are by Republicans, according to the office of the Democratic whip, but the amendment causing greatest concern to the bill's proponents is by a Democrat, Rep. Daniel A. Mica of Florida.

His amendment would permit the CIA to continue financing the "secret war" against the Nicaraguan government on the basis of a new presidential plan for the interdiction of illicit arms to El Salvador, unless Nicaragua formally agrees to stop all aid to anti-government insurgent groups in Central America.

A large number of the Republican-sponsored amendments involve the concept of "symmetry" between U.S. secret aid to anti-government guerrillas in Nicaragua and Nicaraguan secret aid to anti-government guerrillas in El Salvador. GOP strategist Young said the "symmetry" would be the focus of Republican efforts to deal with the bill.

Mica's amendment is considered important because it is sponsored by a Democrat, and thus is more likely to pick up support in the predominately Democratic House.

Mica said his plan is "very close to a consensus almost reached a month ago" by prominent Democratic and Republican lawmakers with representatives of the administration. In the end, most of the Democrats refused to go along with a negotiated arrangement that would have permitted undercover U.S. aid to continue. The negotiations finally broke down on this issue and are considered inactive.

The proposed ban on further U.S. undercover aid to Nicaraguan insurgents, known as the Boland-Zablocki amendment, is co-sponsored by Rep. Edward P. Boland (D-Mass.), chairman of the Select Committee on Intelligence, and Rep. Clement J. Zablocki (D-Wis.), chairman of the Foreign Affairs Committee.

On the same subject, 17 senators, led by Jeff Bingaman (D-N.M.) and Daniel K. Inouye (D-Hawaii), introduced a resolution to place the Senate on record as opposing U.S. funds for anti-government guerrillas in Nicaragua because "it should not be an element of United States foreign policy to see the overthrow of governments with which the United States disagrees politically."

The proposed resolution also expresses backing for the Contadora initiative by several Latin American states, including efforts to negotiate a cessation of arms shipments into Central America by all parties.

The current U.S. course in the area, Bingaman charged, "is starkly reminiscent of the actions of William Walker, the Yankee adventurer, who seized power in Nicaragua in the middle of the 19th century."