David McCurdy is a hawk, a guy who joined the ROTC at the University of Oklahoma during the height of the Vietnam war. He still remembers the heckling he got from antiwar demonstrators.

"They threw water on me because I was a cadet squad leader," McCurdy, now a Democratic congressman from Oklahoma, recalled yesterday. "It made me mad. I thought I was doing my patriotic duty."

McCurdy, 33, still belongs to the Air Force Reserve, and his views on national defense have not changed markedly over the years. The Reagan administration usually can count on the Oklahoma congressman's vote on most defense issues.

But yesterday McCurdy was on the House floor opposing the administration on perhaps the most important national security issue of the year: covert CIA aid to anti-government guerrillas in Nicaragua.

It was not something he did lightly. A second-term congressman with three large military bases in his district, McCurdy is worried enough about charges of being "soft on communism" to have commissioned a poll to gauge voter opinion on the issue.

The way he came to his decision and his reasons for it provide a revealing look at why the Reagan administration's Central American policies have so deeply divided Congress and the American public.

Few members of Congress have had as much intimate contact with the issue as has McCurdy.

As a member of the House Armed Services and Intelligence committees, McCurdy has visited Central America twice in the last two years. He has met dozens of times with top administration officials at the White House, in the Defense Department, on Capitol Hill and at CIA headquarters.

McCurdy originally was receptive to the administration's views. He said he is concerned about the Sandinista government in Nicaragua and "I'm not opposed to covert activities per se." But over the months McCurdy said he concluded, "Either they didn't have a policy or they didn't want to tell us about it."

Top administration officials repeatedly contradicted one another, he said. Administration objectives continually "expanded and shifted."

"There didn't appear to be any single voice or any single policy in this administration," McCurdy said in an interview. "We were getting contradictory reports from everyone."

McCurdy is a boyish-looking, soft-spoken man who keeps matters so close to his vest that Democratic colleagues complain they often don't know where he stands on an issue.

"I never wanted for this to become a partisan issue," he said.

As a hawk and a "Boll Weevil" Democrat, McCurdy was lobbied hard by the Reagan administration. But the effort was sporadic and the cast of players constantly changed.

In unsuccessful efforts to fashion a compromise acceptable to other Democrats, he met at various points with Thomas O. Enders, then assistant secretary of state for inter-American affairs, and Deane R. Hinton, then ambassador to El Salvador, among others. Enders and Hinton were later replaced in their jobs.

McCurdy said he became discouraged when the administration kept adding conditions to ending the covert activity. He said he also became concerned about what he saw as the administration's failure to analyze developments in Central America.

"They decide what is policy and then they go out and get the information to back it up," he said.

McCurdy sent a letter Tuesday to 100 southern Democrats and moderate Republicans, urging them to join him in supporting the Boland-Zablocki amendment, which would end the covert aid, as "the best chance to bring some measure of stability in Central America."

"Many experts, including intelligence analysts, have concluded there is no military solution to the current fighting short of overthrowing the government of Nicaragua," the letter said.

Meanwhile, McCurdy has started to weigh the politics of the matter. He said Republicans in his district have already condemned him because of his stand.

"I think Dave has gotten himself a little out of the mainstream on this one," said Rep. Mickey Edwards (R-Okla.).