The contest for Britain's national election tightened considerably today as Conservative challenger Margaret Thatcher's personal unpopularity continued to erode her party's once commanding lead over Prime Minister James Callaghan's Labor Party.

The Conservatives' lead in the latest public opinion polls ranges from just 2 to 10 percent - down from a range of 13 to 20 percent at the start of the campaign four weeks ago. One poll completed yesterday and published today by the Conservative-leaning Daily Mail newspaper gives Labor a slight lead for the first time.

The Conservatives are still favored to win at least a narrow majority of the seats in Parliament on Thursday. But the polls clearly show that many voters who originally backed the Conservatives and want a change in government are now undecided or intending to vote for the third party, the Liberal, because they do not really want Thatcher to become Britain's first woman prime minister.

Compared to Callaghan, according to the polls, she is seen as inexperienced in government, less capable for high office, out of touch with ordinary people, extreme in her views, condescending and snobbish. The longer the campaign goes on and the more she is exposed to voters on television - around which her professionally packaged, image-conscious campaign has been built - the further she has fallen hehind Callaghan as the poll respondents' preference for prime minister.

When questioned by reporters today about this "Thatcher factor," as it is referred to by pollsters, election analysts and workers in both parties, Thatcher dismissed Callaghan's much greater popularity as an advantage of incumbency. "You tend to get that when personality is merged with office," she said. "I think it will change when a new personality is attached to the office."

While saying that she does not take the polls very seriously, Thatcher has attributed the Conservatives' decline in them to "scares" raised by Labor that her plans to reduce socialism and increase private enterprise would cut off aid to the poor and disabled, put masses of people out of work or create social conflict.

No matter what the polls showed, she said today, she intended "to remain very calm" until Thursday and continue to campaign "on the positive issues we have put forward. We look forward to a splendid victory," she said. "I believe in my heart the people will give us that large, clear majority" she wants "to carry out our policies."

In a jocular, high-spirited press conference at nearby Labor headquarters, where the gloom of recent weeks had given way to giddiness over the latest opinion polls, Callaghan insisted that the Conservatives "ran out of puff some days ago."

He said their "glossy" media-oriented campaign had been geared "for a quick sprint to the polls - vote in haste, repent at leisure. But it hasn't been a sprint. It has been a long-distance race with plenty of time to get behind the glossy surface."

Callaghan and his Cabinet ministers have argued that income tax cuts promised by the Conservatives would be offset by sales tax increases that would hurt lower-income families, that if the Conservatives cut government spending, "half a million people would be thrown out of work in this country" and welfare-state health and social services would be jeopardized.

He said Conservative plans to curb union power would produce worse confrontations and strikes than Callaghan endured this past winter.

But the polls indicate that a large majority of the voters still favor the Conservatives' proposals to cut income taxes and government spending, restrict union power, do more to fight crime, and further restrict non-white immigration. The polls and visits with candidates to various parts of the country reveal an unmistakable desire for change.

This was illustrated on national television last night when Callaghan and Thatcher were questioned separately by the nearly 500 people chosen by random sample as representative residents of Bolton, the northwest England city near Manchester believed to be a demographic microcosm of Britain. Thatcher's answers on taxes, unions, law and order, and immigration were strongly applauded, while many of Callaghan's answers to more antaggonistic questions on the same issues were greeted with silence.

But an opinion poll of a large sample of voters in the Bolton East parliamentary constituency, which has voted for the party winning control of Parliament in the past nine elections, showed the Conservatives' lead over Labor to have falled from 9 percent three weeks ago to 2 percent last weekend. Thatcher has fallen 14 percent behind Callaghan on the question of "who would be the better prime minister."

Tonight, Thatcher went to Bolton for the last major rally of her campaign outside London. She made her strongest attack yet on the Labor Party, arguing that its "nice, cozy democratic socialism" and "most of the older steady men and women who supported Attlee and Gaitskell" had been replaced by "new, sharp doctrine-mongers, the new intolerants. For them, socialism comes first, people afterwards."

Callaghan also has strengthened his attacks on the Conservatives in the campaign's final days, warning last night that it would be "a national catastrophe to elect a Conservative government," meaning "higher prices in the shops, fewer jobs, more strikes, the weakest to the wall."

He said he rejected "the doctrine of privilege and materialism, any doctrine which sets rich against poor, the healthy against the sick, the clever against the slower learners."

Callaghan also made one of his few prsonal references to Thatcher when he departed from his prepared speech to discuss the energetic campaigning of Conservative former prime minister Edward Heath, who was replaced as party leader by Thatcher four years ago.

"Ted Heath, there's a name to conjure with," Callaghan said. "He can't find anything good to say about his leader, so he abuses me."

"I suppose he is trying to climb on the band wagon," Callaghan added, grinning broadly at his obvious reference to Heath's hints that he is available for a Cabinet job under Thatcher. "Well, I warn Mrs. Thatcher, he regards himself as the rightful leader of the Conservative Party. In exile. She stabbed him in the back when he was leader, and he has never forgiven her."

"One slip by her and . . . ," Callaghan said, drawing his hand across his throat.

Thatcher has said publicly that she expects to get only one chance to win an election for the Conservatives because she is a woman, and because she made enemies in wresting the party leadership from Heath.

To prepare herself for the compaign, she studied videotapes of past public appearances and worked to eliminate nervous habits and modilate the once grating pitch of her voice. She both communicated with women voters about homemaking, fashions and makeup in women's magazine interviews, and argued in newspaper interviews that her being a woman should not be political liability.

A poll conducted by Market and Opinion Research International recently about the Thatcher factor showed that although she is less popular with men voters than with women, many voters who dislike her seem to be bothered more by her personality and strident advocacy of her policies than by her sex. Not just Callaghan but also Shirley Williams, a woman Labor Cabint minister, scored better than Thatcher on questions about those traits.