ROCK HILL, S.C. -- Given a great canvas on which to paint his vision of America's future, Vice President Bush readily portrays the mighty and prosperous nation he finds today along the campaign trail.

"I feel strongly about the innate decency and honor of the United States," Bush says in the closing lines of his campaign speech. "We are the freest, we are the fairest, we are the most decent nation that ever existed on the face of the earth, and we have no higher calling than to work for peace and freedom and human rights," he says. "If we don't lead the free world, nobody else can, nobody else will, because they're not strong enough, they're not committed enough."

While other candidates have championed new directions and priorities for the country, Bush begins his quest for the presidency with the central premise that the Reagan years have proven highly successful. He joyfully rips into Democrats who, he says, believe it's "midnight in America." And he happily announces the demise of the "blame-America-first crowd." His loyalty to President Reagan as a mentor and tutor is matched by his unrelenting testament to the nation's stability, prosperity and a resurgence of patriotism.

"This election is really a question," Bush said in one television commercial. "Who can you most trust to continue the Reagan revolution? Who can you rely on to build on what we've done?"

Bush's agenda would "build on" the Reagan years. On the central issues facing the next president, Bush says he would try to finish what Reagan could not -- arms-control agreements with the Soviet Union, backing for "freedom fighters" in Nicaragua and elsewhere, reductions in the federal deficit without raising taxes. On these large goals, Bush seems to be offering essentially a third Reagan term.

Yet, for all their close association, the campaign has shown that Bush would try to reach his aims differently. Bush lacks the natural communications ability with which Reagan launched and nurtured his presidency. Bush is more pragmatic and interested in compromise and problem-solving than the president he has served.

"I am a practical man; I like what's real," Bush confessed in an introspective passage in his announcement address last autumn, in which he seemed to compare himself with Reagan. "I'm not much for the airy and abstract; I like what works. I am not a mystic, and I do not yearn to lead a crusade. My ambitions are perhaps less dramatic, but they are no less profound."

The question about Bush -- raised by his rivals and by other critics over the years -- is whether he could achieve even relatively modest hopes for governing, whether he could truly inspire and lead the nation.

To critics, including his chief rival, Sen. Robert J. Dole (R-Kan.), the vice president seems to have waltzed through two decades of posts, from Congress to the United Nations, from Republican national chairman to envoy to China, from director of central intelligence to the vice presidency, without leaving a mark.

This may be one reason the persistent questions over his role in the Iran-contra affair have stung Bush so deeply, even if they have not seriously hurt his campaign. The questions raised doubts over the very experience and judgment he was advertising as his most basic qualification for the presidency. The Iran-contra affair "wasn't the finest moment in our administration," he acknowledged this week.

Out of the scandal has come an increasingly vigorous thrust in Bush's campaign pitch. He has assailed the "erosion" of presidential power to an assertive Congress. While praising Marine Lt. Col. Oliver L. North as a "national hero," Bush says the Boland amendment, in which Congress barred direct military aid to the Nicaraguan contras, infringed on the president's constitutional authority to carry out foreign policy.

"We do not need 535 secretaries of state," Bush said. A president, he insists, "should be free" to send American troops overseas without declaring war and "without hesitation." Congress, he adds, "has got to tighten its internal discipline, reform the subcommittee structure, establish a joint single committee on intelligence, reconsider intrusive legislation like the War Powers Resolution -- and failure to do so will only endanger the national interest."

On the domestic front, Bush has stumped for an expansion of presidential power, saying that he wants Congress to give the president a line-item veto. Rejected by Congress, the proposal would be taken to the people in a Bush administration, he says, but this often sounds like a tall order for a candidate who is, by his own admission, far less a salesman than Reagan.

Bush has a foreign policy agenda that begins with activist negotiations with the Soviet Union. While Reagan devoted the early years of his presidency to a rearmament program before negotiating, Bush says he would move quickly on a broad range of talks where Reagan has been unable to conclude agreements.

Bush has made the new Intermediate-Range Nuclear Forces (INF) Treaty a virtual cornerstone of his campaign speeches, saying that it demonstrates that the Reagan approach "paid off" with "the first agreement in the nuclear age to eliminate an entire category of nuclear weapons." The next steps, Bush said, are to deal with the quantitative Soviet edge in conventional forces in Europe, to reduce the long-range, or strategic, nuclear weapons and to eliminate chemical and biological weapons.

Unlike other Republicans, Bush says he is eager to move ahead on specific talks even if there remain differences and problems in others. According to one adviser, Bush has been privately impatient with the Reagan administration's approach to arms control. For example, he said, Bush would not just accept the conclusion of experts that there are difficult verification problems with the chemical weapons talks; he would insist that the best experts get together and work out the problems.

"To get these deals we have got to keep the United States of America strong," Bush said. But he acknowledges that the era of Reagan rearmament has passed; even Bush's budget plans call for a plateau in defense spending -- at best.

Bush also vows to carry forward the Reagan doctrine of aiding "freedom fighters" in regional conflicts against Marxism, including the Nicaraguan contras. "We've got to remember the interest of the world is the cause of peace. . . not merely containing communism, but spreading democracy," he said.

On domestic policy, Bush said the federal deficit remains the single most important piece of unfinished business from the Reagan years. He would tackle it with a four-year lid on spending. He said economic growth would be sufficent to bring the deficit down while still allowing most programs to expand to keep pace with inflation. Bush has vowed not to cut defense further, and he has also listed a host of programs he would like to expand -- such as education, drug enforcement, space, and AIDS research. The unspoken bottom line is that some programs would face a hard squeeze, but Bush has avoided saying which ones, except to exempt Social Security.

Bush was never an advocate of the tax-overhaul effort in 1986. He is campaigning to open up the code and restore tax breaks for oil and gas exploration and capital gains income. Despite his 1980 mocking of it as "voodoo economics," Bush has become and remains an avid subscriber to the supply-side theory that some tax cuts generate more revenue for the government than they lose.

"I want to be the education president," Bush has told audiences from Iowa to Florida. His concern for the nation's social ills is often defined in terms of education -- "better schools equals better jobs, better schools equals more opportunity," he says. Except for a proposal to give parents a tax credit for saving for college tutition, Bush has offered little in terms of an education program. What he would most like to do, he says, is use the White House as a "bully pulpit" to encourage excellence.

While remaining loyal to Reagan, Bush has also found it hard to swallow some of the episodes of the Reagan presidency. He often asks rhetorically why Republicans have given up the issue of environmental protection, an oblique criticism of the way it was handled early in the Reagan years. He has also, privately, expressed unhappiness with the ethical lapses that have marred the administration, including the latest investigations of Attorney General Edwin Meese III. He often tells campaign audiences and reporters that he would uphold the highest possible ethical standards, but, in deference to Reagan, refuses to say a word publicly against Meese.