LONDON — WHEN the news came through that the small Social Democratic Party led by David Owen was disbanding, backroom strategists for the opposition Labour Party reached for their pocket calculators. A few seconds of button punching persuaded them that a seismic event of considerable importance had just jolted the British political landscape.
``With skillful handling, we may be able to attract the votes of 4 percent of the electorate, thanks to the SDP's demise,'' said a Labour official. ``That could be the difference between victory and defeat in a close-run general election.''
Labour's leader, Neil Kinnock, was not quite so optimistic, but was still hopeful.
A senior opposition member of Parliament (MP) added, ``Neil thinks David Owen could sway significant numbers of wavering voters to our side, but even that would be worth having. We can't be sure of holding onto our lead over the Conservatives in the next year or so. Every little [bit] helps.''
For Dr. Owen, a member of the original ``gang of four'' that broke away from the Labour party nine years ago to form the SDP, such cold-blooded assessments of his future political role have a bitter taste.
The aim in 1981, he said, had been to ``break the mold of British politics'' by creating a party of the center that would sweep Labour and the Conservatives to the margins.
Instead, in general elections in 1983 and 1987, the SDP failed to achieve a convincing liftoff. Even in an electoral alliance with the Liberal Party, Owen, a former Labour foreign secretary, could not persuade enough voters to switch their allegiance to the SDP.
The last two or three years have seen a steady falling away of the party's membership. Including Owen, the SDP has only three MPs. At a by-election in May, the SDP candidate polled fewer votes than the spoof Monster Raving Loony Party led by a singer called Screaming Lord Sutch.
For Owen, this was the last straw. He called a meeting of the SDP, and at his urging the party decided to wind up its affairs.
``What we did was inevitable. We could no longer sustain ourselves as a national political party,'' Owen said last week. ``But there are still hundreds of thousands of voters in Britain who are fed up with the fudging and mudging of the two big parties.
``What inspired the formation of the SDP is as valid today as it was then.'' Labour strategists are not the only people now paying Owen the compliment of hoping to harvest votes that might otherwise have gone to the SDP.
Paddy Ashdown, the leader of the Liberal Democratic Party (LDP), another centrist political movement, said last week that Owen's supporters would find a ``natural home'' with the LDP.
Owen's pivotal position in British politics as Prime Minister Margaret Thatcher, already 11 years in office, plans for a fourth electoral victory is explained in part by his image as a man of principle who risked his political career by rejecting the policies of the party that in the late 1970s had given him high office.
At that time, Owen was spoken of as a possible future prime minister. His Labour colleagues described him then as thoughtful and ambitious, but also arrogant - a word often still used in reference to him.
A decade ago Labour was under the influence of extreme left-wing groups. Owen decided to quit the party because of its unilateral defense policy, its opposition to Britain's membership of the European Community, and its growing domination by radical left-wing ideologues.
He was joined by Roy Jenkins, a former Labour chancellor of the exchequer, who became the SDP's first leader; Shirley Williams, a Labour education secretary; and William Rodgers, who also was a Labour minister.
Today, Owen takes ``considerable satisfaction at seeing Labour having shifted its stance on all three issues.''
He agrees, however, that Labour's swerve toward the center of politics helped to cut away the ground the SDP might have been able to stand on.
At Labour headquarters, harnessing Owen's considerable political clout by persuading him to endorse the party in the contest against the Conservatives promises to be complicated by resentment over his past attacks on the Labour movement.
There have been reports that Owen would like to rejoin the Labour Party, but he says: ``Many in Labour regard me as a traitor, and that is not the language of comradeship.'' He says he plans to contest the next general election. After that? ``I really don't know.''
In the end, it may be the men and women with pocket calculators who decide how Labour tries to gain maximum advantage from the SPD's collapse and from the moral authority of its leader.
In April, the Gallup opinion poll was showing Labour with a 23 point lead over the Conservatives. The latest poll however gave Labour a 15 point lead.
To be confident of winning the next general election, Labour has to hold on to that margin and, if possible, do better. There are signs of inflation beginning to fall from its 9.4 percent level. That would help the Thatcher forces.
In these circumstances, if Owen were able to persuade only 2 percent of the electorate to vote for Labour, he might deny Thatcher a fourth term and enable Mr. Kinnock, who shares many of his political ideas, to become prime minister.