A smokescreen is being laid down once again by the professional political managers to hide reality from American voters.

The smokescreen: flossy television ads, trivial side issues and claims by all candidates of superior character.

The reality: the certainty that unusually clear decisions about the country's future direction at home and abroad will be made on Nov. 4 whether the voters realize it or not.

Professional political managers prefer the smokescreen, which they can manipulate, to the reality which they cannot; a TV ad can be fine-tuned to attract votes in a way that a firm policy choice never can. But the steady ideological polarization of the Democratic and Republican parties means the presidential election of 1980 will determine the nation's course into the new decade and perhaps well beyond it.

Those issues would be clearest if next summer's conventions made Edward M. Kennedy and Ronald Reagan the presidential nominees. A race between Jimmy Carter and George Bush, each seeming more centrist, would tend to hide differences behind a bland facade. In fact, it really does not matter. Except for two hopefuls without much chance to be nominated -- Republican John Anderson (who usually sounds like a Democrat) and Democrat Jerry Brown (who sounds only like Jerry Brown) -- any November matchup will provide the American voter with exceptionally clearcut choices on these five overriding questions:

1. Will emphasis be placed on trying to restore detente, or will the security of the U.S. be guaranteed through much higher defense spending and new military alliances?

2. Will the federal government embark on an irreversible crash program of radical tax reduction, or will taxes be cut at a much slower rate geared to economic conditions?

3. Will governmental regulation be markedly reduced to promote productivity at the cost of safety, environmental standards and consumer protection?

4. Will the energy crisis be solved by greater stress on production, at the cost of health, environmental and consumer concerns?

5. Will the federal government continue to exert its full weight as an active intervenor behind equalization of employment and education for blacks?

Make no mistake about it: Except for tax reduction, the nominees will not openly debate these questions during the long campaign. That has clearly emerged through the fog of early debate in primary and caucus states.

President Carter, the ardent disarmer, has become a born-again hawk. Sen. Kennedy's crusading liberalism was muted until his Jan. 25 speech. Reagan's rhetoric lost its stridency, at least until his Iowa defeat. All sides are talking strong national defense, reduced regulation and alternative sources of energy. Nobody mentions anything so messy as racial busing or racial quotas.

This is very much in the tradition of American politics. Candidates openly advocating ideologies -- William Jennings Bryan, Barry Goldwater, George McGovern -- habitually lose. In close elections, adversaries intentionally blur their differences. There seemed so little disagreement between John F. Kennedy and Richard M. Nixon in 1960 that, to prove otherwise, Arthur Schlesinger wrote a pro-Kennedy tract (Kennedy or Nixon: Does It Make Any Difference?).

After excoriating Goldwater as a warmonger in the 1964 campaign, Lyndon Johnson won his landslide election and almost immediately sent combat troops to Vietnam -- a familiar spectacle in American politics. In 1932, campaigner Franklin D. Roosevelt not only gave no hint of the New Deal to come but excelled Herbert Hoover in fiscal conservatism with his famous Pittsburgh balanced budget speech. After taking four years of needling, Roosevelt in 1936 ordered speech-writer Sam Rosenman to write a new speech to be given at the identical spot in Pittsburgh that would appear to justify the 1932 effort, but on rereading the old speech Rosenman advised FDR it just wouldn't work. What should I do? asked FDR. Rosenman's answer: Deny you were ever in Pittsburgh!

Even when there is no overt deception, candidates tend to avoid the cutting issues by toying with the exotic. Early stages of the race for the 1980 Republican presidential nomination found Reagan concentrating on a "North American Accord" with Mexico and Canada and Howard Baker calling for a "First Brigade" of elite troops to solve inexpensively the nation's military shortcomings. Presidential debates are particularly prone to exotica: Kennedy and Nixon meaninglessly grappled over Quemoy and Matsu islands; Carter and Gerald Ford bogged down over Polish autonomy.

All this can obscure for the voter the fact that this election will inexorably lead to basic decisions that cannot be avoided considering the country's difficulties at home and abroad. These changes are formed into a partisan matrix by gradual polarization of the parties over the past 16 years. The Republicans have lost their left wing, with liberals fleeing to independent status or to the Democrats following Goldwater's capture of the party machinery in 1964 and Nixon's victory in 1968.

There has been a less visible hemorrhage on the Democratic right, with conservatives who still call themselves Democrats inclined to Republican principles. There is no Nelson Rockefeller or William Scranton now leading a credible liberal wing of the GOP. The Democrats have no successor candidates to George Wallace to follow on social questions or Scoop Jackson to follow on defense policy. Thus, the difference between Carter and Kennedy on the real issues is far less than between them and anyone of the Republican Big Four (Reagan, Baker, Bush, Connally), all of whom are in basic agreement on the issues that count.

How can the voter wade through the fluff and deception to disprove the adage of political sage Mark Shields that unlike selecting a congressman, choosing a president is the least ideological decision made by a voter? To paraphrase John Mitchell, he should watch not what the candidate (or his TV advertising campaign) says in the heat of the campaign but what he has done and said in his past career. That should be easier this time. There is no unknown Jimmy Carter, fresh out of nowhere, in the lists. All the candidates have long public records on which they can and should be judged. t

So, before a single word was uttered in the campaign, the choice for the voter on the five big questions seemed clear: Taxation: Not since the days of the Protective Tariff has there been so universal a Republican theme as comprehensive tax reduction (roughly along the lines of the three-year, 30 percent cut in the Kemp-Roth bill). Actually, Reagan is considerably more enthusiastic about it than his Republican rivals, and all of them are less ardent than many members of Congress. But there is no doubt: A Republican president will be committed to a program of deep, steady tax reduction, both for business and individuals, as a means of regenerating the economy.

Democratic opposition to Kemp-Roth as fiscally irresponsible stems in large part from the conviction that erosion of the tax base will undermine worthwhile spending programs. A Democratic president will reluctantly back far more modest tax reduction, regarding it as a counter-cyclical anti-recession device, rather than basic economic policy. National security: When Soviet troops moved into Afghanistan, the public debate was transformed into a revived contest to become Cold Warrior-in-chief. But beneath the public debate, the choices are profound.

A Democratic president will be anxious to get arms control negotiations back on track, feeling that genuine security in the nuclear age can only come from agreement between the superpowers. A Republican president will spend more for defense, link U.S.-Soviet negotiations to Soviet conduct and seek alliances with anti-Soviet nations, whether or not deficient in human rights. Regulation: This is one of the buzzwords of politics today. Nobody likes it. But whereas the Democrats talk about deregulating the trucking industry to let the truckers fend for themselves, Republicans are talking about less forceful business regulation to protect the environment, the consumer and working conditions -- for the sake of productivity. Although the debate will not be slated in these terms, the election will determine whether the tough regulators brought into government by Carter in 1977 will be replaced by more lenient ones. Energy: The question is not a simplistic one of production vs. conservation; everybody wants more production. But the Republican empnasis is on production of oil, coal and nuclear power at the cost of other considerations -- especially the Clean Air Act and strict nuclear licensing standards. A Democratic president will be interested in curbing the oil companies, at the expense of barrels coming out of the ground. On no issue has the difference been less clearly articulated, but the voter nevertheless will be making this choice for energy policy after next Jan. 20. Race: Neither side wants to talk about it, but differences are profound on an issue that remains central for millions of Americans even if ignored by the news media. A Republican president will not advocate the elimination of "affirmative action" programs, but he will quietly withdraw the federal government as a supporter of special considerations for blacks in hiring and education and may try to tip the Justice Department in the anti-busing direction; he will not, as Carter did, intervene against a Bakke in future reverse discrimination cases. Just as the federal role changed in 1969 and again in 1977, it would again change in 1981.

There is, then, a clear issues profile this year that has nothing to do with age, honesty, experience, candor, charisma or character. Does the country want a president who will cut taxes across the board, increase defense spending and de-emphasize negotiations with the Soviets? Or a president intent on expanding health and safety regulations, continuing full federal intervention to achieve equal status for blacks and limited tax reduction? Unlike 1932 and 1964 there is no reason to be deceived about what's at stake this time.