A prominent Hispanic appointee to President Reagan's National Bipartisan Commission on Central America today expressed deep reservations about the administration's policy in the region, while the White House resisted conservative pressure to remove the other Hispanic from the 12-member body that begins work Wednesday.

San Antonio Mayor Henry Cisneros said he was skeptical about the growing U.S. military presence in Central America and was convinced that it should launch a massive program of economic development there instead.

Cisneros, who is to be sworn in Wednesday with the other members of the commission being headed by former secretary of state Henry A. Kissinger, said Reagan "has not made the case" that a Soviet-Cuban threat warrants the current large-scale U.S. military exercises in the region.

Meanwhile, a White House official discounted a report that the administration would drop from the commission Yale professor Carlos F. Diaz-Alejandro, who has come under fire from Cuban exiles and conservative groups for allegedly being too tolerant of Cuban President Fidel Castro.

"As things stand now, this man is on board, he is not being dumped," a senior White House official said.

"We are keeping this guy unless something turns up that we don't know about."

One conservative member of the administration said somewhat glumly that the White House would just have to live with anticipated dissent from Diaz-Alejandro. But it was apparent today from Cisneros' comments that the Yale professor is not likely to be a minority of one.

"What we have to fear is not the Soviets or the Cubans," Cisneros said in an interview here. He argued that a greater danger is that the United States will repeat what he called the historic mistake of taking a heavy-handed approach to Central America.

"What we do need to fear is continuing a history by which we lose the people," he said. "And that history has taken the form of military intervention, it has taken the form of toppling governments that we don't favor, it's taken the form of economic exploitation by companies, it's taken the form of rigging elections, and I think we just have to fundamentally change our role.

"We are not perceived as a peacemaker, but instead as heavy-handed," he said. "The United States generally is in a poor position to be either the solution to the problem alone, or even to aspire to lead negotiations because of our long history in the region."

Although Cisneros drew distinctions between the Central American conflict and the Vietnam war, he said there is one parallel: The United States runs a risk, as it did in Vietnam, of "alienating the people in huts and villages." If that happens, he said, "the battle is lost and can't be won."

Cisneros, a Democrat who has become one of the leading Hispanic political figures in the Southwest, spoke in his City Hall office. He said no other issue in his 10 years in public life has generated as much mail and debate.

He warned that a deepening military involvement in the region could be more traumatic for the United States than was the Vietnam war.

"If this country allows itself to become enmeshed in a quagmire of military proportions in that part of the world with the attendant bloodshed," he said, "then we will be dealing with a people sharing a very direct cultural heritage with many Americans of Hispanic background."

Cisneros said he begins work on the commission with the view that the United States should respect "self-determination" for Central American nations, even if the result is a distasteful government like the Sandinista regime in Nicaragua.

"If we respect that self-determination then there will be differences when governments that are not our first preference are selected, either on the left or on the right," he said.

He added that the Soviets and Cubans must also demonstrate that they respect this principle of "self-determination."

But he disagreed with Reagan's view that the Soviets and Cubans are exporting Marxist revolution through the Sandinistas. "I fundamentally don't believe that nations are predisposed toward communist solutions," he said.

"Culturally, that's not the case. It's certainly not the role of the church in the region. But we automatically equate anything that has a leftist look about it as Cuban- and Soviet-initiated and many of them simply are not.

"For example, I think the left in El Salvador is not Cuban and Soviet led. And certainly at the beginning, I think much of the Nicaraguan movement was a jelling coalition of forces. I think if you adhere to the principles of self-determination, and the internal processes of Nicaragua result in a junta that has some Marxists at the top, then I think that is something you have to live with."

"I don't believe" the Sandinistas have "crossed the line into total Cuban and Soviet domination," he said, adding later, however, that this question is "a tough call" and a major issue that should be taken up by the Kissinger commission.

Cisneros said he opposes U.S. support of guerrillas seeking to overthrow the Sandinistas and believes the administration acted hastily in ordering military exercises in neighboring Honduras without first exhausting all possible diplomatic solutions.

"I would keep the military a couple of steps back," he said.

Eventually, if diplomacy fails to resolve regional conflict, Cisneros said the United States need not fear the Soviets and Cubans because of the proximity of the United States to Central America.

"A showdown in the Caribbean? That's an American lake," he said of the potential Soviet threat. "It's not going to be a contest. We have the power implicit in our geography and the geopolitics of the region."

Staff writer Lou Cannon contributed to this report.