LONDON, JUNE 4 -- For a man who had announced his political demise the day before, David Owen sounded anything but dead this morning as he discussed the expiration of the small, centrist Social Democratic Party he once hoped to steer to power.

"Politics is a great adventure -- it goes up and it goes down -- and you never know what will happen next," said Owen, speaking by phone from his parliamentary office before setting out on a hectic round of radio and television talk-show appearances. "I suspect I'll still have some influence on what happens after this."

The bad boy of British politics, at once supremely self-confident, charismatic, ambitious and arrogant, David Owen came surprisingly close to his goal of creating a third force to fill the yawning gap created in the early 1980s by the rightward shift of Prime Minister Margaret Thatcher's Conservative Party and the leftward lurch of the opposition Labor Party.

It was only three years ago that polls showed Owen's party, allied with David Steel's centrist Liberals under the banner of "The Two Davids," on the verge of winning enough parliamentary seats to wield the balance of power between Britain's two traditional Goliaths.

The dream died swiftly. Thatcher won by another landslide in 1987, while Steel and Owen finished a respectable but distant third. Afterward, Steel overrode Owen's objections and engineered a merger of the Liberals and the majority of Owen's party into the new Liberal Democrats, leaving Owen and two parliamentary colleagues to stand alone.

Last month, Owen's party finished a humiliating seventh in a special election for a vacant House of Commons seat, outpolled even by something calling itself the Monster Raving Loony Party.

Sunday, at a somber session in a London hotel conference room, the surviving Social Democrats met to declare the obvious: the party was over.

"It was destroying all we stood for to see it become a subject of jokes and derision," said John Cartwright, one the party's members of Parliament. "It's better to put it out of its misery."

Many analysts contend the Social Democrats were victims of their own success -- that both Thatcher's Conservatives and Neil Kinnock's Labor Party responded to the popularity of the alliance by shifting themselves over the last three years to more centrist positions, dramatically reducing the size of the vacuum the newcomers had hoped to fill.

As an editorial in The Independent newspaper put it, "The Labor Party caught Owen bathing in the approval of the public and, in the great tradition of British politics, stole his clothes."

In fact, the centrist dream was always a fragile one. As in the United States, Britain's winner-takes-all system of district voting gives disproportionate representation to the largest party. The Conservatives in 1987 won 58 percent of the seats with only 42 percent of the votes, while the Two Davids polled 23 percent but won 3.5 percent of the seats.

Then there was Owen himself, a brittle and intuitive maverick who even friends say lacked the patience and management skills for the painstaking work of building a political network and who managed to alienate many of his closest supporters.

"Several of David Owen's supporters may feel justified rage at having been lured into a cul-de-sac after following him for understandable reasons of loyalty," said Steel, who added that Owen's opposition to a political merger had cost the new Liberal Democrats "two years of effective life."

Owen, 51, first entered Parliament as a Labor member at 28. Before he was 40, he was foreign secretary and an acknowledged expert in global affairs; polls still show that many voters believe he would make a more competent prime minister than either Thatcher or Kinnock. But Owen and three other prominent party members abandoned Labor in March 1981, declaring they could no longer abide the party's growing leftism.

Owen came to dominate the new SDP, which took a left-leaning line on social and economic policy but a tough stance on defense, supporting both nuclear armaments and British membership in NATO.

The party won support from the young and upwardly mobile middle class -- the "Volvo and claret set" as Yuppies are called here -- but made few inroads among traditional power blocs. Along the way, Owen displayed an independent and combative spirit that won him admirers but also enemies, especially among his former Labor colleagues.

Many gloated over his party's demise, even though Labor's line was that Owen's battalion of supporters, if not the leader himself, was welcome to return to the fold. Some analysts agreed with Owen that Labor must woo the Owenites to validate its new-found centrism.

"I still need a lot of convincing that Labor's conversion to their new policies, which are mostly our old policies, is for real," Owen said today. "Kinnock can't win unless he convinces a substantial number of people -- and I am one of them -- that his conversion is genuine."

As for Thatcher, whose policies he generally abhors but whose personality he sometimes admires, Owen says she is still likely to win the next election, but by a much smaller margin.