On the threshold of the critical early tests in his presidential campaign, Vice President Bush is still dogged by the unanswered questions and apparent contradictions over his role during the gravest foreign policy blunder of the Reagan presidency, the Iran-contra affair.

Before the latest revelations about Bush's knowledge of secret arms sales to Iran, questions were being asked by his rivals for the Republican nomination, by journalists and by independent counsel Lawrence E. Walsh. Since the clandestine arms sales were first disclosed in 1986, Bush has never given a full public accounting of how he fit into the puzzle of secret deals and failed policies.

Instead, he has given partial accounts, saying he never talks about his private advice to the president. "I'm not a kiss-and-teller," he said this week when asked about what he knew.

While public opinion polls show that concern over the scandal has receded in the minds of many voters, it remains a potential political trouble spot for the vice president. His aides fully expect, for example, that he will be confronted with the issue at Friday's GOP debate in Iowa, as he was at the last Republican debate.

The questions about his role go directly to what Bush has described as some of his greatest assets as a future president -- his experience in intelligence and diplomacy, his concern for ethics in government, his loyal service to President Reagan, his leadership in devising a strict policy against making deals with terrorists.

Former secretary of state Alexander M. Haig Jr. said last month in a speech pressing Bush for answers about his role in the affair, "He's running for president now. The American people are entitled to know what position he took during this storm that imperiled our nation's vital interests."

"Where was George Bush during the storm?" Haig asked. "Was the copilot in the cockpit, or was he back in economy class?"

If Bush were truly a participant in all the major decisions of the Reagan presidency, as he has said, how could he have been "out of the loop" during the Iran arms sales decision process, as he has also said? If Bush were a seasoned professional in diplomacy and covert operations, as he has advertised, how could he sit through hour upon hour of meetings on an operation that violated the administration's policies and may have violated the law, and not object?

Bush has faced similar questions repeatedly in recent weeks. On the campaign trail in New Hampshire yesterday, the questions came again from voters. He has answered them indirectly, saying that he generally supported Reagan, that he had some "reservations" about the Iran arms sales, that he would not trade weapons for hostages, that "mistakes were made." And he has invoked the confidentiality of his discussions with Reagan as a reason not to "fine tune" the details of his role in the affair.

Bush recently added an unspoken twist to the questions about his role by inviting two key figures to his annual Christmas party -- former national security adviser John M. Poindexter and Lt. Col. Oliver L. North, the fired National Security Council staff member. Both men are targets of Walsh's criminal investigation and have acknowledged destroying key documents and evidence in the Iran scandal.

The vice president also has responded to questions about his role by calling attention to the report of a task force on combating terrorism that he chaired in late 1985. "It is the best antiterror report that a country has," Bush said this week.

But the counterterrorism effort also illustrates the problems for Bush created by the Iran-contra affair. The decisions made by the president and his top policymakers to ship arms to Iran in hopes of winning the release of American hostages were directly in conflict with the policy being developed by the Bush task force -- that the United States should not make concessions to terrorists.

Over a period of several months, Bush seems to have advocated one policy publicly and consented to another privately.

The terrorism task force was set up in the aftermath of the TWA hijacking in 1985. The study was written virtually the same time that Reagan and his advisers were grappling with the early clandestine Iran arms sales through Israel. The 14-member task force of senior U.S. officials and staff dealt with a broad range of U.S. policies toward terrorism and repeatedly emphasized that concessions should not be made to terrorists or states that sponsor them.

For example, in its final report, the task force criticized private "individuals and companies" that have "paid ransoms to terrorists for the return of kidnaped employes or stolen property. Such action is in direct conflict with the national policy against making concessions or paying ransoms to terrorists."

The panel said the U.S. government "will make no concessions to terrorists. It will not pay ransoms, release prisoners, change its policies or agree to other acts that might encourage additional terrorism." At the same time, it said, the United States would use "every available resource" to gain the safe release of American hostages.

As these words were written by the Bush task force, ransom was paid to terrorists with the approval of the president, as several witnesses testified to Congress last summer.

According to retired admiral James L. Holloway III, who was executive director of the antiterrorism task force, Bush never informed that panel of the secret arms sales to Iran or that some of the weapons shipments were made while the policy against concessions to terrorists was being reaffirmed by the task force.

"We knew nothing about ongoing operations," Holloway said. He said the task force focused on "policy questions" and did not examine actual covert operations. Holloway said this week that the Iran arms sales were "inconsistent with that policy" laid out in the task force report, but that sometimes operational necessity forces a temporary change in policy.

The Iran arms sales initiative began in August 1985 and shipments were made in September and November of that year. By December, there were heated debates over the project at the White House in Reagan's presence. But the vice president missed a key Dec. 7, 1985, meeting at which objections were raised by others because he was at the Army-Navy football game in Philadelphia.

One former administration official, who asked not to be identified, recalls that Bush introduced Holloway to others on a train en route to the game from Washington that day, praising him for his work on the terrorism task force.

At the White House that morning, however, Reagan was faced with angry objections from then-Defense Secretary Caspar W. Weinberger and Secretary of State George P. Shultz. Weinberger said the arms deals with Iran would violate U.S. laws; Shultz said they would violate U.S. policy against making deals with terrorists.

Although Bush has said he was excluded from some key meetings, by the time the terrorism task force report was made public in March 1986, the vice president had attended several sessions with the president at which the still-secret arms deals and related hostage release were discussed.

Publicly, however, Bush continued to promote the no-concessions-to-terrorists theme. "Our policy is clear, concise, unequivocal," he told reporters March 6, 1986. "We will offer no concession to terrorists, because that only leads to more terrorism."

Bush was also asked directly about the hostages in Lebanon, but responded only vaguely to reporters that day by saying their capture indicated the "insidious nature of international terror" and adding that "what we hope is that these recommendations will facilitate stopping terrorist actions."

In a speech the following month explaining the U.S. bombing raid against Libya, Bush said, "We must make the price so high for the terrorists and those who give them comfort that they will abandon this cruelest of warfare."

At the same time, North and others were laying plans for former national security adviser Robert C. McFarlane to visit Tehran on a plane carrying U.S. weapons for Iran.

Bush has said he had "reservations" about the extent to which the Iran arms deals were carried out by Israel. However, there is no evidence that Bush raised questions or doubts about other controversial aspects of the operation -- including the president's decision to withhold notice to the congressional intelligence committees for at least 10 months.

Bush has repeatedly held out his service as director of central intelligence as one of his leading credentials for the presidency. In the wake of the congressional investigations of the Central Intelligence Agency by the Church and Pike committees, Bush was well aware of the sensitivity of congressional notification, former agency officials said.

A former CIA official who worked closely with Bush said, "He recognized there was no way for the agency to operate without the cooperation of those committees, and notification was a requirement . . . . It was the point about which the Congress felt strongest and if there was going to be trouble, it would be over this issue. Notification provisions and requirements mattered most."

During Bush's tenure as CIA chief, on May 19, 1976, the Senate passed a resolution setting up the Select Committee on Intelligence and calling for strict notification procedures. Though it did not have the force of law, the resolution said the committee should be "fully and currently informed" of all intelligence activities, including "any significant anticipated intelligence activity." This language was later incorporated into the 1980 Intelligence Oversight Act and is current law.

Bush made dozens of appearances on Capitol Hill. Donald P. Gregg, Bush's current national security adviser and a 31-year CIA veteran, has said that Bush's tenure at the CIA was "to reengage, recommit the agency to responding to Congress" and that Bush emerged from his time there with a belief that "covert action only works when it's very limited in time, scope and purpose."

But the Iran initiative did not meet these standards. The time, scope and purpose shifted repeatedly. There is no evidence in all the investigations and reports on the Iran arms sales that Bush sought to impose any changes on the operation beyond his "reservations" about relying on Israel.

In his autobiography, "Looking Forward," published last September, Bush acknowledged indirectly that his previous standards had been ignored. "What lesson can future presidents learn from Iran-contra?" he asked. "An old lesson that's all too often forgotten: Don't look for shortcuts, and don't try to circumvent the process. Most important of all, follow the rules. Rule one is that in planning and carrying out a covert operation, the law has to be followed to the letter. Rule two is never try to strike a bargain with terrorists."

In the year since the Iran initiative was first disclosed, Bush has often ducked questions about his role, or used vague language to explain what happened. In his speech to the American Enterprise Institute last Dec. 3, Bush said, "I was aware of our Iran initiative, and I support the president's decision." But Bush said then that he was not aware of any "ransom payments" or circumventing of "the will of the Congress and the law."

Asked Dec. 19 when he supported the president, Bush said, "I'm not going to help you one way or the other."

When the Tower special review board issued its report depicting Reagan as detached from the management of his policy, Bush said, "If the president had been told of some of the things that are in that report, they wouldn't have happened. But he was cut off . . . . So I'd love to say, with the benefit of total 20/20 hindsight, that in my infinite wisdom I could have stopped it, but I don't think that's fair. I think I see things in that report that I never would have permitted to happen, and I know the president feels the same way."

The report, he added, "makes very clear that I wasn't involved in some of the things people consider wrong."

Later, Bush said, "I wish . . . that I had known that we were trading arms for hostages . . . and then I would have weighed in very heavily with the president . . . . "

In his autobiography, Bush devoted a few pages to the scandal, saying he suspected that he had been left out of key meetings. He wrote that "at no point along the way, from its beginning to its end," was the full National Security Council membership "formally brought together to discuss the Iran initiative. Not one meeting of the National Security Council was ever held to consider all phases of the operation . . . . "

In fact, Bush attended a "full NSC meeting" on Jan. 7, 1986, at which Shultz and Weinberger aired their objections, according to the congressional Iran-contra report.

After the congressional report was published, former secretary of state Haig pressed Bush in the Dec. 1 NBC debate to say how he advised Reagan during the Iran affair.

Bush dodged the question. When Haig protested that "you haven't answered my question," Bush concluded: "Time's up."