While the rest of Britain struggles with severe blizzards, scattered strikes and the uncertainty about when beleaguered Prime Minister James Callaghan will call a national election, Scotland and Wales face a more historic if less dramatic moment of decision.

In referendums on March 1, voters in Scotland and Wales will decide whether they want the first limited form of self-government that Britain has offered them in centuries.

Even though the home rule plans fall far short of separate nationhood for either Scotland or Wales, the referendums' results will determine the future of separatist movements that made big political gains during the 1960s and 1970s in the two anciens Celtic kingdoms.

As an odd side effect in this year of political melodrama here, the referendums may also help decide how much longer Callaghan remains prime minister of all of Britain.

Callaghan's Labor Party government is now in its fifth and final year and a national election must be held by the beginning of November.A winter of strikes and bad publicity has left Labor far behind the rival Conservative Party in opinion polls and Callaghan does not want to risk an election much before October.

Because Labor does not hold a majority of the seats in the House of Commons, Callaghan depends on the votes of small regional party representatives, including 11 Scottish Nationalists and three Welsh Nationalists, to avoid losing a vote of confidence that would force an immediate election.

If large enough majorities in Scotland and Wales vote "yes" for home rule in the referendums, the Labor government will move in Parliament to create the Scottish and Welsh assemblies authorized in the home rule legislation passed last July. While this process goes on, it is likely that the Scottish and Welsh Nationalists in Parliament will continue to help keep Labor and Callaghan in power through the summer.

It is far from certain, however, that voters in Scotland and Wales will approve the home rule measures.

Not only must a majority of those voting approve the home rule plan, but the number voting "yes" must also equal or exceed 40 percent of the total number of eligible voters. If the "yes" vote reaches the 40 percent mark in either Scotland or Wales, the Labor government is committed to putting the home rule plan into effect in that region.

If the "yes" vote falls short of 40 percent of the electorate but still constitutes an overwhelming majority of those voting, the Labor government is expected to try to implement home rule anyway, in part to hold onto the Scottish and Welsh Nationalist votes in Parliament.

Public opinion polls in Scotland show that those intending to vote "yes" for the home rule plan still greatly outnumber the likely "no" votes, but the gap has been narowing. In Wales, the most recent poll showed "no" voters in the majority but heavy campaigning began only recently.

Keeping the outcome of the referendums in doubt are the history of the Scottish and Welsh separatist movements, the current political atmosphere in Britain and the watered-down nature of the home rule plans themselves.

Wales has been united with England and ruled by the English monarchy and Parliament since the Middle Ages. The thrones of Scotland and England were first occupied by the same monarch in 1603, and in 1707 the Act of Union made Scotland, too, a part of Great Britain under a single British Parliament.

Separatist movements in Scotland and Wales in theis century were mostly ignored in London until the Welsh and Scottish Nationalists began winning seats in Parliament and making strong showings in districts where the Labor Party in particular long had been dominant. After the Labor Party came to power in 1974, it began to draft a home rule plan that would give Scotland and Wales just enough self-government to deflect the separatists' appeal.

Under the plan being voted on Scotland and Wales would each have an elected assembly that would make policy and spending decisions in such areas as education, health, housing, highways and economic development. However, the assemblies would not be able to raise taxes and the size of their budgets would be set by London.

The Scottish assembly would also have the authority to pass laws in these areas, subject to a British government veto. The Welsh assembly would not have this legislative power. Wales appears to have been offered less home rule because the Welsh Nationalists have not done as well in elections as the Scottish Nationalists and therefore are less threatening.

Although they are disappointed with the amount of home rule being offered, both the Welsh and Scottish Nationalists are campaigning hard for approval because they believe that the proposed assemblies eventually could lead to complete self-rule.

Many Scottish and Welsh voters, however, oppose separation from the rest of Britain and may vote "no." Their fears are being fed by home rule opponents, including many Conservative Party leaders, who warn that voting "yes" would be taking the first step toward dividing Britain.

The Conservative Party historically has opposed shifts of power from Parliament to any region of Britain. Furthermore, the proposed Scottish and Welsh assemblies likely would have Labor Party majorities.

Other opponents point out that while English legislators no longer would be able to vote on many strictly Scottish matters that would be taken over by a Scottish assembly, Scottish members of Parliament still would have a vote on everything affecting England.

Meanwhile, Labor Party leaders argue that the proposed Scottish and Welsh assemblies are a good substitute for separatism rather than a Trojan horse for it.

Prime Minister Callaghan warned at a recent campaign rally in Scotland that rejection of the home rule proposals would only add to the frustration upon which separatism feeds.

"If the present opportunity is missed," Callaghan said in Glasgow, "the issue would become the property of the extremists who advocate independence. They would seek every opportunity and have every excuse to exploit every grievance. They will try to divide Scotland, whereas [voting "yes"] can unite Scotland without dividing her from the rest of the kingdom."