The Protestant Ulster Unionists are demanding major concessions for Northern Ireland from British Prime Minister James Callaghan as their price for helping to keep Callaghan's minority Labor Party government in power.

At stake is not only whether Callaghan will have to call a national election now or when he prefers, in October, but also whether the British government is going to be forced to follow the dictates of the Protestant Unionists in ruling divided Northern Ireland.

Ulster Catholic leaders -- joined on St. Patrick's Day by Irish-American politicians led by Sen. Edward M. Kennedy (D-Mass.) and House Speaker Thomas "Tip" O'Neill (D-Mass.) have already accused the British of what a Kennedy-O'Neill statement called a "conspicuous tilt" in favor of the Protestant majority.

Several key Ulster Unionist members of Parliament have signaled that they will continue to support Callaghan only if his government returns some home rule to Northern Ireland and spends $200 million to send cheap British natural gas to Ulster through a pipeline under the Irish Sea.

"If the government offered to build a pipeline to give us the benefit of natural gas," said Harold McCusker, Ulster Unionist member of Parliament, last week, "some of us might say that it might well be worth repaying them."

Enoch Powell, who has emerged as the leader of seven Ulstenist members of Parliament, including McCusker, who hold the fate of Callaghan's government in their hands, demanded both the gas pipeline and a shift from London to Belfast of control over education, health, housing, social services and other governmental functions in Northern Ireland,

Callaghan's government fears the gas pipeline would be a wasteful way to supply energy to Northern Ireland, which already can produce enough electricity to satisfy all its needs. Britain also is not ready to give Ulster more home rule until the Protestant majority is willing to share power with the Catholic minority.

However, the Callaghan government has been kept in power by support in Parliament from Scottish and Welsh nationalists and the Ulster Unionists, and it is likely to be deserted by the Scottish and Welsh nationalists soon.

The Scottish Nationalist Party has warned that it and the Welsh nationalists will join Labor's major opponent, the Conservatives, in trying to bring down Callaghan's government in a a vote of no confidence if Callaghan does not bring a plan for limited home rule for Scotland to the floor of the House of Commons for debate and a vote before the end of the month.

Callaghan has been stalling because the Scotland home rule plan has no chance of being approved in Parliament after Scottish voters gave it only lukewarm support in a referendum two weeks ago.

Callaghan could still narrowly win a vote of confidence in Parliament, however, if the Ulster Unionists led by Powell continue to vote on Labor's side. Callaghan has kept their support thus far by pushing through Parlaiament a bill that will increase the total number of Northern Ireland seats in Parliament from 12 to 18, most of which would likely be filled by Protestant Unionists.

"Now that the battle for parliamentary parity has been won," Powell said over the weekend, "local democracy for Ulster is the crucial issue. It will be the touchstone by which we shall tell our friends from our enemies, and sound policies from perilous ones."

Referring to the efforts that both Labor and the Conservatives will now be making to woo him and the Unionists for the showdown vote likely to take place before Parliament adjourns for its Easter recess, Powell added, "In the coming weeks, the Ulster Unionist Party in Parliament will be vigilant to miss no opportunity for genuine advance."