IRA's political drive worries its own 'old guard' and Britain

Provisional Sinn Fein, the political wing of the illegal Irish Republican Army (IRA), is intensifying its campaign to win votes in Ireland and to lay the foundation for a left-wing republic to include the North and the south.

Confirmation of this came at an annual meeting in Dublin last week. The increased political thrust will threaten the position of the mainly Roman Catholic Social Democratic and Labor Party (SDLP) in the North.

James Prior, British secretary of state for Northern Ireland, warned at a private meeting of conservative members of the British Parliament that an upsurge of Sinn Fein and the demise of constitutional Catholic representatives could lead to Ireland becoming the ''Cuba'' of Europe.

Two years ago the philosophy of the Provisional Republican movement was outlined at the annual conference by Belfast delegate Danny Morrison. He asked: ''Who really believes that we can win the war through the ballot box? In this hand, we take power in Ireland.''

The latest conference underlined the theme. Gerry Adams, a Northerner who recently took over the presidency of Sinn Fein, outlined the group's future political strategy. But he also paid tribute ''to freedom fighters - the men and women of the IRA.''

Undoubtedly, Adams and the new, tough strategists from the North have moved Sinn Fein to the left. But already there are hints of strain within the movement as the ''old guard'' questions the new policy. The Belfast leadership wants to take part in local government elections and in the poll for the European Parliament. In particular they want to challenge the SDLP as the voice of the Roman Catholics in the North.

Already Sinn Fein has narrowed its margin of popularity to a 5 percent difference (SDLP 18 percent, Sinn Fein 13 percent) during the June elections to Westminster. Adams won the West Belfast seat from longtime nationalist Gerry Fitt. Recently a survey by the BBC suggested that in the next local government elections in the North, Sinn Fein could take many more seats.

Whether this electoral impetus will force the Sinn Fein ''old guard'' to hold its hand is not clear, but the veteran campaigners are not happy. They believed they had the agreement of the younger men to boycott political assemblies like Westminster and the European Community, but they regard a last-minute decision by last week's conference to allow successful Sinn Fein candidates to take their seats in Europe as ''an act of treachery.''

The new Sinn Fein strategy also puts pressure on the IRA to modify its campaign of violence. It was stressed in secret sessions at the Dublin conference that indiscriminate attacks involving civilian casualties would cost the movement valuable votes in its coming election campaigns. Nevertheless, the current policy of attacking Northern Ireland's security forces and part-time soldiers, most of whom are Protestants, will continue.

This further alienates the Protestants, whose representatives show no willingness to deal with the SDLP, which desperately needs to show voters some evidence of its ability to give Roman Catholics a meaningful role - if it is to ward off the challenge from Sinn Fein. This particularly worries Secretary of State Prior, who fears that if Sinn Fein takes over the SDLP role in the North, it could have a ''knock-on effect'' in the south.

He suggested to a private meeting of Tories at Westminster that because of the worrying state of the Republic's economy, a Sinn Fein and Provisional IRA upsurge there could - in the worst possible scenario - lead to a ''Cuba-type country off the west coast of Europe.''

Later Prior's aides tried to play down his comments and said that he did not believe a Cuban-style takeover was likely. But a spokesman said, ''He used the possibility to illustrate the dangers facing the Republic, if the SDLP's position in the North were further damaged by Sinn Fein.''