Washington — The Democratic dilemma is the apparent strength of President Reagan. As he nears the end of his third year in office, a widespread judgment here is that he has brought certain strengths to the presidency after the Carter years and will be a formidable incumbent to beat in 1984 - assuming he runs. If the election were held today, many believe, Mr. Reagan would have the edge.
Not just Republicans hold this view. Many Democrats and presidential scholars come to the same conclusion. They note that an economic downturn or a foreign policy disaster could quickly alter Reagan's fortunes by the time the election rolls around.
But they see a number of factors working in the President's favor at the moment, factors that turn less on the substance of policy than on the qualities of leadership. Among them:
* He has greater personal popularity than did Presidents Carter or Ford. He is generally liked and trusted because of his geniality, decency, and simplicity.
* Because he knows what he wants, he has provided a sense of direction and stability, whatever people may think of his policies. His optimistic nature and his stress on ''hope'' rather than Carter-like ''malaise'' have helped boost public confidence.
* He has demonstrated that, without abandoning his ideological views, he is capable of political flexibility and compromise and therefore is not hidebound by ideology.
* He has shown political skill in working with Congress and has conveyed the sense that a strong leader can break through governmental stalemate.
* He is a good communicator of his policies.
Such an assessment does not disregard the weaknesses or the potential pitfalls of the Reagan presidency. Republican leaders themselves point to a number of vulnerabilities: the perception among many that the administration has not been fair to the poorer segments of society but has favored the rich and privileged; the failure of the President to win a broad coalition of support among blacks, women, environmentalists, and other segments; and the high social cost of the US military buildup.
''Society has been forced to pay a high cost - in education, research, environment - in order to strenthen the military base,'' says Charles Doran of Johns Hopkins University. ''The hope is that the economy will be invigorated and enable society to replace some of what has been lost, when growth returns. But will the economy perform well enough?''
Moreover, Dr. Doran says, Reagan's economic program has entailed considerable redistribution of wealth, and, while the poor still have a safety net under them , people in the middle class have seen their lot slip.
''The middle class was told the tax cuts would help, but they have not yet seen the benefits,'' he says. ''How soon before they rebel?''
It is also recognized that Reagan has yet to score a major foreign policy success, although the invasion of Grenada and the reassertion of American power it implies seem to have gone over well with the majority of Americans. Mr. Carter during his brief tenure in office chalked up an impressive array of diplomatic achievements, including the Panama Canal treaty, a SALT II agreement, and the first step toward peace in the Middle East.
But, unlike Carter, political observers say, Reagan has made a dent in the public mind where it counts most: conveying a sense of can-do leadership on the domestic front. Carter left office with the inflation rate soaring at more than 12 percent and an impression of confusion and unpredictability. Now inflation is down and there is a greater sense of steadiness.
''Carter was erratic,'' says Democratic pollster Peter Hart, ''while Ronald Reagan knows where he is going'' and that has helped him.
Comments a Democratic political operative: ''Reagan has exhibited leadership. He has done the things he said he would. He's not a great President, but he's not a bad one. It (1984) could be a real contest.''
Even foreign policy could redound to his benefit, in the opinion of some.
''If Grenada is in the limelight in 1984, you may have a hard time beating Reagan,'' says Sen. Dale Bumpers (D) of Arkansas. ''Whenever there's a foreign adventure, this plays well to the electorate.''
''I doubt foreign policy will be a factor, but it's unpredictable,'' comments scholar James L. Sundquist of the Brookings Institution. ''In time of crisis a president can exert strong leadership, and that can benefit him.''
Administration officials refer to the Reagan presidency as having effected a veritable economic revolution. The slashes in government spending, the sweeping tax cuts, and the reduction in government regulations are all seen as having turned the country away from the New Deal and Great Society path of government growth.
But there is a difference of opinion as to just how much of a revolution this has been.
''This is less a reversal of the New Deal than a presidential pause over it, '' says scholar Thomas Cronin of Colorado College. ''Reagan has raised questions regarding entitlements and subsidies, and he has cut the rate of growth of government. But the tax system is loaded with deals, the bureaucracy has actually increased, and the deficits may choke off the recovery. Reagan has failed here.''
Dr. Cronin places credit for the economic changes less with Reagan than with the fact that a conservative tide was running in the country generally.
''Jimmy Carter should not have been elected,'' he says, ''and some of the success of Ronald Reagan is due not to himself but to the fact that Nixon was not a conservative and to the fact that for seven years the country had been welling up against regulations and taxes.''
Where Reagan has been succeessful, Cronin says, is in bringing a ''Hamiltonian energy'' to the presidency, in communicating well, and in the force of his character.
''He has high self-confidence,'' Cronin comments, ''and that is important for a nation. Nixon, Ford, and Carter did not project it. Reagan knows who he is and likes life - like Kennedy and FDR.''
These intangible qualities could be decisive in 1984. ''So much of what goes on is a matter of psychology and that has to do with public and business confidence,'' suggests Stephen Wayne, a political scientist at George Washington University. ''Reagan has excelled as a symbolic and psychological leader - letting people feel good about themselves so that the forces that make for change can be released.''
''When we became hopeful, we worked out of recession,'' Dr. Wayne adds. ''Reagan may not have created the victories, but he has presided over them.''
One criticism often made of the President is that he has a shallow understanding of the world and makes no attempt to educate himself in the complexities of issues. He is said to prescribe simplistic solutions based on an old-fashioned view of things. But even this is seen to have its political advantages. ''Reagan was elected not because of his views, but because he knew where he was going,'' says Wayne. ''Simplicity is appealing to the electorate. Reagan can reduce a problem to its lowest common denominator, and people understand. To the average person, he makes sense. From a symbolic point of view , Reagan is the 'right stuff.' ''