Ronald Reagan likes to break things. He has this reputation as a sweet, good-hearted fellow you'd love to have as a neighbor or as a pal. A nice guy who walks old ladies across the street and helps kids learn their Scout knots.

But you look at his record, and you see he breaks things. Since he became president, he broke the back of the Democratic resistance in Congress and he broke almost 50 years of expansion of the welfare state. He broke Congress to his fiscal discipline the way a wrangler breaks a colt to the saddle.

He doesn't brutalize. He applies force cleanly, leaving his victims to say, in Tip O'Neill's words, "No hard feelings, old pal." But break them he does.

Last week he set out to break the air traffic controllers' strike and bust the union that called it. A union, incidentally, that endorsed him for president.

What nobody seems to notice is that, for Reagan, the action was perfectly in character. He rarely blusters. He doesn't fight dirty. But he lets nothing stand in his way.

Back at the beginning of his political career, in 1966, he bowled over two nice guys -- Republican George Christopher and Democrat Pat Brown -- who made the mistake of thinking this actor was a pushover. They never knew what hit them.

Two years later, he set his sights on the presidency. The prospective nominee of his party was fellow-Californian Richard Nixon, a man regarded as a martyr and a hero by many Republicans who thought he unfairly had been counted out of the White House in 1960. Reagan was not one of those sentimentalists. He did everything in his power -- right up until roll-call time -- to break Nixon's grip on the nomination.

In 1976, he came right back seeking the same prize. This time, the Republicans had a president. His name was Jerry Ford. A lot of Republicans, including some of Reagan's own financial and political backers, thought Ford deserved a chance for a full term. Not Reagan. He fought until the last vote was counted in Kansas City to break Ford's lease on the White House.

In 1980, for many observers, the key break in the campaign came in Nashua, N.H., on the Saturday night before the primary. Reagan had lost to George Bush in Iowa, and had agreed with Bush to a one-on-one dabate in Nashua. Bush kept the commitment; Reagan broke it. He showed up with four other Republican contenders, demanding they be included, and so flummoxed Bush that the erstwhile front-runner was never the same again. A lucky break? If so, it was one Reagan contrived.

Jimmy Carter thought he could sidestep Reagan's uppercuts, but in the Cleveland debate's closing round, Reagan nailed him cleanly and left him on the deck.

The same go-for-broke approach has characterized his presidency. He offered Congress a "partnership," but it quickly became plain that it would have to be on his terms. When the year began, the expectation was that the tax and budget bills would be hammered out between the Democratic House of Representatives and the Republican Senate, in a consensus process reflecting the mixed verdict of the 1980 election.

But three times, Reagan rejected the counsel of compromise and put the House through his personal political wringer -- breaking away enough Democratic defeactors to leave the oppostion party demolished, its leadership in disarray. The bolters said they were afraid to oppose Reagan, and the President raised his champagne glass in triumph.

Then came his first bout with a labor union. Critics had complained that Reagan had no policy for controlling wage inflation. They were wrong. His policy is the oldest of all: union-busting.

The controllers were perfect for his purpose -- a small union of highly paid government employees, performing a service that was specially vital for Reagan's business and middle-class constituency. If 15,000 welfare workers had walked off their jobs, Reagan might not have filled the Rose Garden with his righteous wrath. But with this union and this strike, he was guaranteed applause.

Citing the no-strike pledge in the controllers' contract, Reagan moved in the first hours of the strike to end negotiations, decertify the union as a bargaining agent, impound its treasury and jail its president. "He's tough as nails on this," an anonymous aide said somewhat unnecessarily. Within 48 hours, those who remained on the picket line were being permanently discharged from their jobs and facing a presidential blackball on any future government employment.

As in most of the previous instances of his career, Reagan managed to make his "break-the-so-and-sos" stance very popular politically. His niceguy character is so deeply etched in the public consciousness that nobody seems to notice his grip on the adversary-of-the-moment's windpipe.

In this sense is very much in character with his dealings with George Christopher, Pat Brown, Dick Nixon, Jerry Ford, George Bush and Tip O'Neill.

The message is getting around: Don't mess with this guy. Whatever gets in his way, he tries to break.