Growing pressures for changes in the leadership of the counterrevolutionaries fighting the leftist government of Nicaragua broke into public view yesterday as the House took up the Reagan administration's request for $100 million in military and economic aid for the guerrillas.

Arturo Cruz, one of three top civilian leaders of the contras, as the guerrillas are known, added his voice to those of disappointed conservative U.S. supporters of the rebels who are seeking changes. Cruz said he cannot remain in the contra leadership unless reforms he is demanding are made.

The impact the dissension within the overall guerrilla organization will have on the aid debate in Congress is uncertain. But conservative congressmen have told President Reagan that their positions are being undermined by the apparent failure of the contra leadership to deal effectively with rising allegations of mishandling of funds and criminal activity by some contras and human-rights abuses within Nicaragua by the guerrillas.

Cruz is part of a triumvirate -- with Adolfo Calero and Alfonso Robelo -- heading the rebels' umbrella organization, the United Nicaraguan Opposition. He said in a telephone interview here that he has met "staunch opposition" within the grouping to reforms he proposed that he believes would ensure more democratic decision-making and smoother handling of the financial and military affairs of the contras.

The opposition, Cruz said, came from "a small group within the FDN," or the Nicaraguan Democratic Force, the largest contra guerrilla army with an estimated 15,000 fighters, led by Calero. Cruz, a politician, controls no troops, while Alfonso Robelo, a Costa Rica-based businessman, controls a force of about 350 guerrillas in southern Nicaragua.

Cruz said he is demanding three changes in the procedures of the umbrella grouping. He wants decisions to be made by "majority vote, not consensus," because he said his and Robelo's views often were bypassed. He urged that all U.S. government aid to the movement, whether public or covert, be administered by the United States to avoid questions about the handling of the funds.

Cruz is also demanding to be better informed about the contras' military operations, and to have more say in the choice of military targets.

"I'm not demanding that anyone resign," Cruz said. "I'm not blackmailing anyone." He said there has been "some distancing" between himself and Calero, but they are "still in communication." While Cruz is not considering resigning now, he said if the reforms are not carried out he will "do what I have to do."

Cruz, Calero and other contra leaders were in meetings yesterday with Assistant Secretary of State Elliott Abrams. "Elliott put down the word," an official said, "that in response to the pressures from all sides we are going to have to see a change in their leadership style."

The administration official said that FDN leaders had committed themselves to "serious negotiations" to "democratize."

Cruz's demands come amid growing pressure for changes in the contras' leadership, with much of the criticism centering on Calero. Some of the pressure is emanating from several U.S. conservatives who broke with Calero and other FDN leaders in recent months.

Several disillusioned contra backers brought their charges in recent weeks to members of Congress, including both supporters and opponents of increased U.S. aid to the contras. Three Democratic representatives who favor some form of aid, led by Charles W. Stenholm (D.-Tex.), asked President Reagan in a meeting last Thursday to investigate allegations of corruption by contra leaders and respond in writing, Stenholm said. The office of Sen. John Kerry (D.-Mass.), who opposes the aid, also is gathering information about the allegations.

Stenholm said concerns were expressed to him by four different U.S. contra supporters that senior contra leaders -- particularly Calero -- had misappropriated privately raised funds. He labeled these accounts as "allegations" but said he took them seriously and believed that the information he provided to Reagan has been confirmed.

Calero missed two interview appointments with The Washington Post over the last week due to illness, according to his aides. He did not return numerous phone calls.

Calero, a former Coca-Cola executive in Nicaragua, was described last week by State Department officials as a persuasive and hard-working manager of the contras' operations. Calero, Cruz and Robelo were lauded last month at the White House, when Reagan referred to them as "the future of Central America."

Administration officials, who also have been pressing for changes in the contra movement, said they would like to see Calero remain at the head of the umbrella group, but also would like to work more closely with other leaders to broaden the contras' base of support.

In the past year the administration channeled virtually all of its $27 million in nonmilitary aid through the guerrilla grouping, to encourage all the groups fighting the Sandinistas to unite. But officials said in interviews over the past two weeks that the administration has moved to a new approach of "letting 100 flowers bloom," as one official put it.

Under legislation approved March 20 by the Senate but which has not passed the House, the administration would provide $100 million in military and economic aid to several groups and urge them to coordinate their military campaigns. Officials stressed that the aim is not to undercut Calero, but to diversify the contras' leadership..

The legislation that passed the Senate also calls for reforms by the contras to improve their human rights performance.

A principal source of conservatives' complaints against the Calero leadership is Philip Mabry, a conservative activist from Fort Worth, Tex., who said in a telephone interview Saturday that he raised a total of about $35,000 in clothing and medical supplies for the contras in the past 18 months.

Mabry said that Calero and his brother Mario -- who is in charge of shipping to Central America most goods collected for the contras in the United States -- abruptly refused to cooperate with several supporters seeking to gather funds or supplies.

Being cut off without explanation raised the supporters' suspicions that their donations might not reach followers in Nicaragua and embarrassed would-be fund raisers with local conservatives who offered to contribute, Mabry and other supporters said.

Stenholm said of Mabry, "His credibility is very high with me."

Reached by telephone Sunday night, Mario Calero described Mabry as a "crackpot." He said Mabry had repeatedly promised to collect supplies for the contras but "he lacked the part of delivery. If he says he ever gave us anything, he's a big liar."

Procontra conservatives in California and Texas said they became wary of Calero after they were asked by one of his representatives to help purchase weapons in the United States for a contra hit-team to operate here and in Central America.

A Californian businessman, who described himself as a longtime conservative activist but who asked that his name not be used out of fear of retaliation, said he organized four trips to California for Calero last year and offered to raise $1 million for nonmilitary activities of the anti-Sandinista cause before Calero stopped dealing with him in mid-1985. He said in a telephone interview Saturday that Calero attempted to circumvent him to deal directly with potential donors of money contacted by the businessman. He also said Calero conducted an arms transaction in his presence in June 1985 that he objected to, when Calero accidentally left a hand grenade on the seat of his car.

Richard McColl, a Kerry aide who met extensively with the businessman here last month, said, "Across the board he was an articulate and credible person who didn't want to see any damage to the contra movement."