IT'S GOING to be ugly out there this fall.

Ask an expert.

Edward J. Rollins, the jolly director of the Republican Campaign Committee, told a campaign and elections seminar last week that "1990 is going to be a tough, tough, aggressive campaign season -- maybe the bottom of the barrel, with hard-hitting, negative campaigning."

That's depressing, but there's something worse: The reason nastiness is on the rise is that nastiness works. Hear conservative Patrick Buchanan, an alumnus of the Nixon White House where the slash-and-burn philosophy prevailed: "Democrats have learned the lesson of '88. The way to defeat the tactics of Atwater and Ailes is to emulate the tactics of Atwater and Ailes, and escalate."

It's a dismal prospect, bad for the country, bad for democracy. Voters are turned off. In 1988, only 50.l6 percent of the eligible voters turned out on election day. In the last off-year election, 37 percent made it to the polls.

"The turnout could go below 30 percent this year," said Rollins.

One of the things adding to the acrid air of this campaign is the smell of burning cotton. It arises from that lamentable issue, the flag-burning amendment. George Bush, who explored pretty much the limits of demagoguery in 1988, is at it again. We must have a flag-burning amendment. He is bringing to a virtually non-existent nuisance all the urgency that would be better applied to the genuine problems before him. "It's an American issue," he said, trying to prod Congress to pass the amendment before the Fourth of July. It's like using a nuclear bomb on squirrels who raid your bird-feeder.

But for Republicans, it is good sport. It tortures Democrats. It lends itself to the 30-second spot. Never mind that the First Amendment has been our shield for 200 years, that the Bill of Rights is the glory of our national documents -- as Senate Majority Leader George Mitchell says, "the most eloquent, the most effective statement of individual liberty in all human history."

The Supreme Court, for the second time in two years, struck down as unconstitutional a law banning flag-burning, summoning the flag-wavers to the ramparts once again.

Rollins gave a little demonstration of the mischief Republicans can do with the flag. A questioner who is opposed to the flag-burning amendment asked how to handle the issue.

Rollins grinned as he gave the quick and dirty reply, which will probably be echoed on a hundred platforms when the leaves begin to fall. "If I were a strong advocate of flag-burning . . . ," he began.

His questioner broke in. "I'm a strong advocate of free speech. How can I be inoculated on the issue?" Rollins declined to advise him on any snake-bite remedy since he plans to use the issue copiously in the campaign -- although he is not sure it will be so central by then.

In the summer of 1988, the flag was a hot topic, too, and helped Bush make the case that sober, pedestrian Michael Dukakis was a closet McGovernite.

In Dukakis's home state, the First Amendment took another beating earlier this month. An episode worthy of Watergate occurred and raised questions about just how dirty the tricks are going to be from now on.

Massachusetts Democrats assembling for their convention in Springfield were met with a picket line of policemen who tried to bar them from entering the hall.

The local police union, keenly pro-Bush, had settled a dispute with Springfield Mayor Mary Hurley the night before. If Hurley agreed not to speak at the convention, they would take down their picket line. But the next day it was back up again, and the reason given was that the mayor had had the temerity to enter the hall. The intervening event, according to Democrats, was the arrival on the scene of Ron Kaufman, a White House operative known for zealotry. He is quoted as having said, "I'm totally innocent, but it sure was fun."

Despite Kaufman's denial of involvement, the Democrats are quite rightly suing him -- and a top aide to a GOP candidate for state treasurer. The complaint: violation of their civil rights. The state chairman, Rep. Chet Atkins, says he has videotape of policemen pushing and harrassing delegates and at one point standing with locked arms to prevent them from entering the hall for five hours.

Constitutional authority Laurence Tribe of Harvard Law School says the trial, if it ever comes to pass, could provide valuable insights into the politics of thuggery.

Disrupting the Massachusetts Democrats, a thoroughly divided and dispirited lot, is in a class with messing up the Constitution to stop flag-burning. Only an instinct for excess could be the motivation.

Mary McGrory is a Washington Post columnist.