DES MOINES, JAN. 8 -- Vice President Bush tonight opened the first confrontation with his Republican rivals of the new year by sharply attacking criticism of his role in the Iran-contra affair, insisting he had "answered all questions" except for disclosing his private advice to President Reagan.

Bush again vowed to keep confidential that advice. His emotional defense came not in response to challenges from his opponents but at the outset of a televised debate when questioned about his role by the moderator, James P. Gannon, editor of The Des Moines Register.

"I have answered every question put to me, save one. The question is, 'What did you tell the president of the United States?' " Bush said. Looking sternly at Gannon, Bush admonished, "Your paper had a full page this morning suggesting that I didn't answer questions."

"I resent it frankly, and I think you owe it to me, you owe it to me to ask a question that I haven't answered," Bush said. The vice president confronted the issue head-on tonight after being dogged all week by questions about what he did during the gravest foreign policy crisis of the Reagan presidency. Once Bush fired back at Gannon, however, the issue faded and did not dominate the debate, as many had expected.

The two-hour debate, held one month before the Feb. 8 Iowa caucuses, was sponsored by The Register. It is regarded as the most important event before the caucuses and came at the end of a week in which two polls showed Senate Minority Leader Robert J. Dole (R-Kan.) holding a sizable lead over Bush in Iowa.

Dole seemed almost at times left out of the action tonight as the other candidates centered attention on the vice president. Bush was questioned on energy taxes and prices by Rep. Jack Kemp (R-N.Y.), on leadership by both former secretary of state Alexander M. Haig Jr. and television evangelist Pat Robertson, and on the new arms-control treaty by former Delaware governor Pierre S. du Pont IV.

On the Iran-contra affair, Bush reiterated that he did not know about the diversion of funds to the Nicaraguan contras. "The Congress had a $8 million or $10 million hearing. They never suggested I did. The Tower Commission didn't suggest I did."

Speaking of the Iran arms sales, Bush said, "If we erred, and I think we did in retrospective, a deal that wasn't supposed to be arms for hostages proved to be that. But if we erred we erred in trying to free Americans held by terrorists. Yes, I'm sorry things didn't work out right."

Bush added, "I don't think its fair to say I haven't responded to questions." Bush demanded that Gannon give him an opportunity to respond to the other candidates who have been "shooting at me."

Bush's role in the Iran-contra affair came up again as the Republican contenders questioned each other. Haig pressed Bush on whether he should reveal what advice he gave to Reagan and asked whether his refusal to do so would make him vulnerable to Democratic attacks in a general election campaign.

Bush fired back that he had already said publicly that he had concerns about relying on a third country in the operation, which he has in the past identified as Israel.

"Of course we had concerns," Bush said of himself and the president. "But I supported it, and I don't see the vulnerability of being the standard-bearer" for the party. "I don't see it," he insisted.

Then, seeking to turn the tables on Haig, Bush asked, "What did you tell Mr. Nixon in the days of Watergate? Or did it take you 15 years" to reveal it.

In questioning each other, the Republicans also reignited their argument over the treaty to eliminate intermediate- and shorter-range nuclear missiles in Europe. Bush spoke out for the treaty, calling it a "great step for peace." Dole, who in the past had qualified his support of the pact signed last month by Reagan and Soviet leader Mikhail Gorbachev, also declared his support for the pact and said he will lead the ratification effort in the Senate.

But du Pont and Robertson renewed their harsh attacks on the treaty. When Bush asked du Pont whether he had changed his view since the last debate, the former Delaware governor replied sternly, "I'd vote no, George, and I don't support it."

Du Pont cited the Soviet numerical advantage in conventional forces in Europe as making "the defense of freedom in Western Europe more difficult." Du Pont recalled statements by Reagan that the Soviets had changed their world outlook and no longer seek world domination and said, "I think he's dead wrong. . . . I don't believe the communists have suddenly become noncommunists."

Du Pont claimed that Bush is "eager" to get on with the next treaty limiting intercontinental nuclear missiles but said, "I'd like to see the Soviets fulfill commitments to existing treaties first."

Robertson, too, refused to support the treaty. "We aren't reducing nuclear arms at all," he said. He added that the treaty leaves open the prospect of a huge conventional force buildup that could cost $100 billion. And he expressed concern that without the medium-range missiles there would be a focus on the intercontinental missiles. He suggested the specter of "bombs . . . falling in the mainland of America."

The Republicans also clashed over energy taxes. Bush said that he opposes an oil import fee, while Dole supports it. Kemp then challenged Bush on why the Reagan administration has not accomplished other goals such as eliminating the windfall profits tax and deregulating natural gas.

Bush shot back the administration had "sent up the stuff" but Congress had not approved it. Kemp said he had prevented the administration from wiping out tax breaks for the oil industry. Bush then called for more "incentives" in the tax code for the oil industry, a position that he has taken in private deliberations in the administration but rarely talked about publicly.

Kemp accused Bush of urging the Saudis to raise oil prices, and at one point quipped that the vice president is trying to make Texas, his home state, "a member of OPEC." Bush insisted that he had not done that, but also said he thought it was wrong that oil prices had fallen too low.

For the most part, the Republicans asked each other questions taken from each others' campaign speeches, sticking with familiar themes such as education, health care for the elderly and economic opportunity.

But Bush's temper flared when Haig quoted him as saying recently that the first thing that came to his mind after he was shot down in the Pacific during World War II was the separation of church and state. "What I said was my mind turned to faith and God and family," Bush said. He accused Haig of making a "cynical" attack and said, "This seems like a low blow to me."

Robertson earlier tried to use a question to Haig to get the former secretary of state to go after Bush, a major Haig preoccupation in recent weeks. Noting that as a Cabinet member, Haig had an insider's view of the Reagan administration, he asked, "Tell us about the leadership of the vice president. Was he really the leader he says or did he {Reagan} turn to Bob Dole, like he says."

Haig, seemingly embarrassed, scratched his head. He said that a secretary of state never talks about what he tells a vice president, and that it was not his role "to render a report card" on Bush's vice presidency.

In one section of the debate, Rep. Patricia Schroeder (D-Colo.), who considered becoming a candidate for her party's nomination, questioned the GOP hopefuls. She said she should not be thought of as "the Democratic pit bull" because "pit bulls don't cry," a reference to the public tears she shed when announcing she had decided not to run for president.

But Schroeder did find a way to needle almost every one of the candidates. She told Kemp, for example, that she had a more conservative voting record on spending issues than he did.

He replied that he received a bad rating from the National Taxpayers Union because it included defense spending increases, which he supported, in its rating system.

"I'm not a hawk. I'm a dove," he added. "Heavily armed, but a dove."

She told du Pont that when he served with her in Congress "you had a good strong moderate voting record. What happened?"

"I went home to become governor and I had to learn to lead," he replied. Du Pont also turned to the GOP's and his advantage a question about the more than 100 Reagan appointees who had "left office under an ethical cloud."

Du Pont shot back that the "most recent example of sleeze" was Sen. Edward M. Kennedy (D-Mass.) putting a bill through "in the middle of the night without hearings" to make someone sell a newspaper," a reference to legislation that would force Rupert Murdoch to sell the Boston Herald. He also charged that 10 Democrats in Congress were under investigation for ethical violations and that House Speaker Jim Wright (D-Tex.) "has had charges placed against him in the press."

Under questioning from Schroeder, Dole said he would freeze all government spending for a year if elected; Haig said he would work to reduce waste in defense spending, and Bush called for all his GOP rivals to make public their income tax returns for the last 10 years.

The Republicans used their closing statements to offer voters a picture of themselves much like the one they have been describing in recent months on the campaign trail and in paid advertising.

Dole stressed his roots in Middle America and his "small-town traditional values," as well as his experience in Washington. He rattled off a list of legislation where he said he had made a difference -- social security, voting rights, tax reform. Dole said if he is the victor in the Iowa caucuses he would want to believe it was because voters here looked "at this guy from Kansas" and "they said to themselves, 'Bob Dole, he's one of us and that's why he won . . . .' "

Haig said all the other contenders were qualified to be president in "normal times" but then added acerbically, "These are not normal times." He added, "Indeed, business as usual in the White House will not be tolerable." He said the nation no longer could survive "incompetence" and "malfeasance," and suggested he would be the most qualified to sit across the table from Gorbachev and "match him every step of the way."

Kemp sounded themes of economic prosperity and opportunity, saying the Republican Party should attempt as it once did to include blacks and other minorities. He outlined a goal of "exporting democracy and capitalism to the rest of this waiting world."

Robertson decried the "runaway deficit" of the federal government, "the breakup of the American family," what he described as epidemics of drugs and crime, "and now an AIDS epidemic." Robertson said Congress and "government insiders" had "made a mess of things" over the last two decades, and he emphasized his experience in founding the Christian Broadcasting Network and a university.

Bush said the nation has an "unfulfilled agenda" from the Reagan years. He reviewed his resume, from his war record to his jobs in diplomacy and politics, and said, "On vision, you have to have a vision. Mine is that education should be the No. 1 thing." He added, "I want to be the president that wrestles the deficit to the ground . . . . I want to be the president not afraid to reach out for peace."

Du Pont categorized the others as "Washington insiders" and said if that is what voters want they should choose Bush because "he's held practically every job there."