LONDON, JUNE 12 (FRIDAY) -- Margaret Thatcher was awarded a historic third consecutive term as Britain's prime minister this morning, as her Conservative Party was returned to power with a likely majority of more than 100 seats in the House of Commons.

With only a handful of the country's 650 parliamentary districts still to report, the Conservatives neared a landslide of proportions approaching their 1983 majority of 144 seats. Pre-election polls had indicated a small Thatcher victory, or even a hung Parliament in which no party emerged with a working majority.

Thatcher, who was comfortably reelected as a member of Parliament by her own London district of Finchley, appeared early this morning to wave to well-wishers from the window of Conservative Party headquarters near the palace of Westminster.

It was left to Conservative chairman Norman Tebbitt to deliver the party's verdict. "I'm very pleased indeed," Tebbitt said with characteristic understatement. "We seem to have got a much better result than most people thought."

In terms of percentage of the total vote, the Conservatives appeared likely to match their 13 million total, or 42 percent, of 1983. The main opposition Labor Party appeared set to increase its 1983 total of 8.5 million by about 1.5 million, for 32 to 33 percent.

The vote was a major setback for Labor and its leader, Neil Kinnock, who had hoped at worst to limit Thatcher to a majority of no more than 40 to 50 seats.

Labor appeared unlikely to increase its parliamentary share by more than two dozen seats. The result was one of Labor's worst showings in 50 years, second only to the disastrous result of 1983, when the party won only 209 seats.

But the biggest loser of the night was the third-place Alliance of the Social Democratic and Liberal parties, whose final portion of the vote fell substantially below the 25 percent it won in 1983. The Alliance appeared likely to suffer a net loss of at least one of the 27 seats that it held going into the election. Liberal Party leader David Steel called it "a very disappointing night."

Although Thatcher emerged victorious, the vote seemed to prove Kinnock's contention throughout the campaign that Britain is fast becoming two separate countries, divided economically and politically between the prosperous south and the destitute north.

In Scotland, the Tories lost at least eight seats to Labor, leaving them with possibly as few as five Scottish members of Parliament. Two of Thatcher's Cabinet members who hold seats in Scotland, Scottish Secretary Malcolm Rifkind and Defense Secretary George Younger, squeaked by, with Younger being reelected by only 182 votes.

In the coal mining districts of Wales, Labor picked up at least three Conservative seats.

The Conservatives made up a good portion of the loss, however, in the English Midlands and in inner London, where they had targeted left-wing Labor candidates as dangerous extremists.

The election, in which a record 43.2 million Britons were eligible to vote, brought several notable new faces. Among them were the first three blacks ever elected to Parliament, all from the Labor Party in London seats.

One of them, lawyer Paul Boateng, noted in his victory speech that the road to Parliament had taken blacks "400 years . . . We went before as humble petitioners. Never again. We go now as tribunes, socialist tribunes who are defenders of their rights."

New Labor winners also include David Blunkett, a blind local government leader and rising force within the party, who will become the first member of Parliament to attend with a guide dog.

A record 35 women were elected to parliamentary seats.

Among the more prominent individual losers were Shirley Williams and Roy Jenkins, two of the four founding members of the Social Democratic Party, which formed as a breakaway from Labor in 1981. Williams failed to defeat the incumbent Conservative in Cambridge, while Jenkins, a former Cabinet officer in several Labor governments, lost his seat in Scotland.

Thatcher had called the election "the clearest choice in my lifetime." Considered a particularly nasty battle, even by the normal standards of personal attack in British politics, the campaign was based on two starkly contrasting portraits of the country.

The Conservatives, who described Labor as controlled by left-wing extremists and advocating a defense policy that amounted to surrender to the Soviet Union, ran on a slogan of "Britain Is Great Again. Don't Let Labor Ruin It." Thatcher painted a picture of a country that, under her stewardship, had been brought back to economic health and stability after the years of decline and union strife under Labor in the late 1970s.

Over and over, Thatcher noted that by most economic indicators -- inflation, interest rates, the low level of public-sector borrowing, massive overseas assets -- Britain was again a world economic leader.

She promised more of the policies that have formed the basis of her eight-year record -- legislation to curb the power of trade union leaders; the privatization, or denationalization, of remaining state-owned industries; continued lower inflation; lower taxes and a strong, nuclear-based defense.

Kinnock and Labor, however, described a different Britain -- with more than 3 million workers unemployed and an ever-widening gap between the haves and the have-nots. Through increased public spending, financed by higher taxes and increased government borrowing, Labor pledged to create 1 million jobs during its first two years in office.

Labor analysts believe that, if anything lost them the election, it was the party's policy of unilateral nuclear disarmament. In post-mortems already being compiled, there have been hints that Labor moderates will press for the policy to be altered.

The size of Thatcher's majority will have a significant bearing on both her future and that of Kinnock.

Based on predictions of a massively decreased majority, a number of senior Conservatives, including members of Thatcher's Cabinet, had privately expressed concern that she would become an increasingly divisive influence both in the party and the country. There were predictions that Thatcher, who must be elected as party leader each fall by the Conservative conference, might be replaced within 18 months after the election.

But the size of the Conservative vote will likely reduce any potential challenge to Thatcher's power and appears to greatly increase the prospect that she will serve a full five-year term.

For the Labor leader, a defeat of modest scale could have been turned into a victory of sorts, positioning him for the next race. But the rout Labor suffered is likely to embolden challengers to his leadership in the near future.

The future of the Alliance appeared in doubt. A number of independent analysts attributed its poor performance to its two-headed leadership and predicted that there would be an early move to merge the two parties.

Having won only 27 seats in 1983 despite its 25 percent of the vote, the Alliance had campaigned for reform of Britain's electoral system, proposing a change to proportional representation. But the strong Alliance vote four years ago was largely attributed to Labor's weakness. With Labor this time winning back much of its traditional hard-core constituency, one analyst noted, the Alliance was caught in "an absolutely classic third-party squeeze."

While arguing that "disaster is too strong a word" for the Alliance results, Social Democratic Party leader David Owen said this morning that "the honest answer is that neither the Labor Party nor we have been able to dent the Conservatives."