Back in 1967, the Glasgow suburb of Hamilton made political history here, sending Winifred Ewing to Parliament, the first Scottish Nationalist elected since the war.

Over the next 10 years, the Nationalists enjoyed unbroken success. Their demand for an independent, sovereign Scotland was widely interpreted as the beginning of the breakup of the United Kingdom. They collected 11 seats in the last election and, in the polls, threatened to overtake Labor as Scotland's premier party.

Wednesday night in Hamilton, however, it became clear that the Nationalist tide has reached its peak, that the party has gone as far as it is likely to go. The Nationalists' best vote-getter, Margo MacDonald, bright and magnetic, went down to a crushing defeat there in a byelection. To rub in Labor's triumph, Hamilton is MacDonald's hometown as well as the launching pad from which her party took off.

Labor's man, George Robertson, not only held the seat but doubled the 3,300 vote edge that his party had recorded at the last general election in October 1974. Only two months ago, the attractive MacDonald, deputy leader for the Nationalists, was thought to be a shoo-in.

Virtually every commentator here said MacDonald's loss made clearer than ever that Prime Minister James Callaghan will call a general election in October. Yet those close to him are far from sure. It appears that Callaghan's preference is for an election early next spring.

The defeat in Hamilton is the third recent setback for the Scottish Nationalists. In mid-April, Labor won another byelection in Glasgow by a comfortable margin, holding onto a seat the Nationalists had counted on winning. A few weeks later, the Scottish Nationalist Party fared badly in local elections.

None of this means that the Nationalists and independence are finished. Yet it does appear that the party's momentum has been broken, that it can count on about three Scottish voters in 10 and no more. The imminent breakup of the United Kingdom now seems no more likely than that other recent scare, the imminent collapse of the British economy.

It is apparent that most Scots do not want to leave Britain. There is plenty of dissatisfaction with what Scots regard as their second-class status, with an unemployment rate well above England, with the remoteness of Whitehall government.

Prime Minister James Callaghan and the Labor government, however, have deflected at least some of this by a bill to give Scotland limited home rule. This so-called "devolution" measure is now working its way through the House of Commons and has clearly blunted some of the Nationalists appeal.

Callaghan's management of the economy has also won ground for Labor despite a jobless rate in Hamilton alone of about 10 percent. Callaghan is convincing a growing body of voters that his party has ended the economic crisis in Britain and holds out the best hope of stabilizing prices and adding jobs.

Among the factors Callaghan must weigh when deciding the timing of a general election is the fact that Labor is a minority goverment and could be outvoted 323 to 306.

Next November, the Commons must be counted on a motion of confidence when the Queen's Speech - a state of the union address outlining the proposed legislative agenda - is voted upon.

Between now and then, Callaghan will be counting noses carefully. He will be determining whether he can pick up enough votes from other parties to support the program and carry on to the spring; whether he should go down to defeat on Labor's chosen agenda and call an election in the late fall; or whether he should avoid the Commond vote and hold his election in October.

On the strength of the Hamilton and the Glasgow byelections, he can rest more easily, give himself the luxury of choice. MacDonald's fall ends Labor's nightmare, a fear that the Scottish Nationalist Party could slice in half Labor's bloc of 36 Scottish seats.