For Democrats, '84 field is set, but all else is uncertain

This week the last two members of the six-man Democratic presidential field - Sens. Ernest F. Hollings of South Carolina and John Glenn of Ohio - officially take to the road.

The prospect ahead for the Democratic contenders is much like a cross-continent marathon - a road with emotional highs and lows, desert stretches, a winter in the great plains of Iowa and in New Hampshire's Appalachians.

Uncertainty abounds. The candidates' strategists say that some might drop out. They don't know for sure what pace the rival team's leader, President Reagan, will set - or even whether he will actually take to the road again, despite his Republican handlers' hints that he will.

In any event, 16 months before the 1984 Democratic National Convention, the preliminary Democratic nomination field is set. Senator Hollings announced Monday in South Carolina, and Senator Glenn is scheduled to announce Thursday in Ohio.

Here is how pros in both parties size up the race:

Democrats rate former Vice-President Walter Mondale ahead of any one of the other five Democrats - Florida's Reubin Askew, Sen. Alan Cranston (D) of California, Sen. Gary Hart (D) of Colorado, plus Hollings and Glenn. But Democratic professionals say Mr. Mondale is likely to be overtaken before the convention, although it's unclear who will overtake him.

Republicans, likewise, say Mondale is off to the fastest start. But they add they are not sure he will overcome the latent strengths in his competitors.

''Mondale just about has to have a lock on it (the nomination),'' says Stuart Spencer, a Reagan political strategist. ''He has a lot of IOUs to collect.'' But Glenn also has great potential, Mr. Spencer says. Still, Glenn may lack political savvy to take advantage of it.

''Does Glenn know what he's up against? Does he know the ropes?'' Mr. Spencer asks. Hart could be a surprise. ''Hart could do well in New Hampshire,'' Spencer says. ''He knows the game.''

Reagan's current slight rise in the polls, like his pulling even again with Mondale and ahead of Glenn in hypothetical voter match-ups, says little about the play of issues and personalities likely in the more critical months a year hence.

''All there's been is Reagan in the news,'' a Democratic strategist says. ''The economy's getting better and he's getting the benefit of the change in hope. Hope alone won't do it for them. They have to sustain the recovery. Even an economic recovery won't do it for them. There's a whole range of issues - the environment, arms control, civil rights at home, human rights abroad - where Reagan's vulnerable.''

Reagan benefits by the failure so far of the Democratic contenders to catch the public's imagination on these alternate issues.

''The Democratic rank and file are saying they're just not getting any message at all from their party's candidates,'' one Democratic strategist complains. ''This is a big missing ingredient with our constituencies. You're seeing - with the restlessness for a black candidate, the nuclear freeze, environmentalists, women, labor - all are showing signs they want to get going for 1984. The Democrats aren't motivating these people. They're not igniting their enthusiasm.''

The Reagan White House runs a risk with its current emphasis on foreign affairs and defense. Concerns that Reagan will involve the United States in a war are rising, mostly among women. Observers in both parties and on Capitol Hill say Reagan - with hard-liners, national-security adviser Bill Clark, and Defense Secretary Caspar W. Weinberger - could involve the US too deeply in Central America or take such an inflexible stand in arms talks with the Soviet Union that the talks could break down. What kind of opening such events could give the Democrats is hard to guess. But at least it would provide a reading of Reagan's leadership in ways now unforeseen.

If he runs again, Reagan is still accorded the edge for '84, if only because of the advantages of incumbency. Early electoral vote trial heats, however, show Mondale or Glenn running well against Reagan.

Reagan thus far has managed to avoid the familiar third-year presidential skid in the polls. He is actually about where President Carter was in early 1979 before gasoline lines and economic pressures undercut public approval of his performance. Even in the summer of 1979, when only 3 in 10 Americans approved of the way Mr. Carter was handling his job as president, the public still showed high regard for him as a person.