When she warned Britain a few years ago about "the growing danger of Soviet expansion," Margaret Thatcher said at a campaign rally here Thursday night, "the Russians said I was an iron lady."

"They were right," she declared, as her audience roared its approval. "Britain needs an iron lady!"

Exuding confidence as fresh public opinion polls this week showed her party still strongly leading in the campaign for Britain's May 3 national election, Thatcher taclkled head-on the only issue that apparently can prevent her from becoming Europe's first woman prime minister - Margatet Thatcher herself.

The polls reflect overwhelming acceptance of the Conservatives' contention that "It's time for a change" and a move to the right in Britain. Two of every three British voters continue to tell the poll-takers week after week that they are dissatisfied with the Labor Party, which has governed the country for 12 of the last 15 years, and its policies of expanding government involvement in the economy and the rest of society.

A large majority of voters want to vote Conservative, the polls show, because they like Thatcher's promises to cut taxes, government spending and the cost of living while curbing trade union power, enforcing law and order, restricting nonwhite immigration into Britain and strenthening the military against any future Soviet threat. The give the Conservatives a commanding 10 percent of the polls with less than two weeks left in the campaign.

But many of these Conservative leaning voters, including a disproportionately large number of men, are not yet certain about Thatcher - about whether they want a woman, about her combative personality, her rigid right-wing views and her sometimes harsh-sounding statements on sensitive issues.

Although they give her high marks on the job she has done as leader of the Conservatives in opposition, they still rate her behind incumbent Labor Prime Minister James Callaghan in readiness to serve as prime minister, national leadership, judgment under pressure and ability to get along with ordinary people.

"There is real enthusiasm behind the Conservatives this year because of taxes, prices and the strikes," said a middle-aged male Conservative Party worker on the edge of a crowd swarming around Thatcher, 53, in a shipping center in the town of Coalville, northeast of Birmingham in the industrial Midlands. "But some of the men are lukewarm especially those between about 40 and 60. There is a feeling among them that a man would have been better."

"Most of the men I know will vote Conservative anyway because they want to see a change," said a camera store owner as Thatcher went by. "But they would have preferred a bloke."

Women are much more enthusiastic about her, according to polls and party workers. It was mostly women who pushed excitedly through the crush around Thatcher int he shopping center to touch her hand and wish her good luck.

"It's time a woman got the chance to try running the country," said a coal miner's wife, repeating an argument Thatcher makes repeatedly herself. "We control the purse strings at home; we know the value of money and how to handle it."

The party worker who reported that some middle-aged Conservative men were uncertain about Thatcher also said he liked her himself because "she is such a remarkable woman, intelligent and very tough."

Thatcher is gambling that this toughness, which helped her emerge from the middle ranks of Conservative front-benchers in Parliament to take over the Party's leadership four years ago, will win her more votes than she will lose at a time when Britain appears to be searching for a new past week after having begun the campaign with uncharacteristic demureness.

"I gather from the radio I am called a reactionary," she told Conservative Party Workers in the Welsh city of Swansea. "Well, there is a lot to react against."

"I seek confrontation with no one," she said in a speech about the party's promise to curb the power or unions. "But I will always strenuously oppose those at home whose aim is to disrupt our society and paralyze our economy, just as I will always stand up to those who threaten our nation and its allies with attack from abroad."

When a reporter asked why her London press conferences were held at the same time each morning as Callaghan's, she patiently explained how she had tried to persuade Labor to alternate with her in going first each morning. They refused, she said, looking the reporter firmly in the eye, "and I'm not going to be pushed around by anyone."

Thatcher repeatedly reaffirmed this week her controversial assertion last year that many Britons felt "swamped" by black and Asian immigrants from elsewhere in the Commonwealth and defended her pledge to restrict future entry.

The subject was first brought up on radio and television phone-in shows by complaining immigrant callers. Thatcher then added it to her major campaign speech here in Birmingham, where many nonwhite immigrants live.

"Yes, we are going to be very strict on immigration control - very strict indeed," she told an Asian caller on a nationwide television phone-in program last night. The caller charged that Thatcher's immigration plans were "cynical" and "divisive."

"I do not accept that," Thatcher answered. "We have a lot of immigrants in this country, accepted for permanent settlement here, like yourself. But if we were to go on and on taking more and more and more into this country when we already have unemployment problems, which are particularly bad for our young West Indians, that would be the very worst thing we could do for racial harmony."

"I don't retreat in any way from what i have said on this. We must have strict control on all future immigration. I believe it is in the best interest of our immigrant population who are permanently settled here to know that there won't be more and more and more coming in."

Prime Minister Callaghan responded today by saying the Labor Party would not "play on people's fears" about nonwhite immigrants.

"What Mrs. Thatcher has failed to bring out," he said, "is the very tight control on immigration which exists now" and the fact that "there is not a substantal number arriving now."

In a well-organized media-oriented campaign, Thatcher also is trying to show voters another side of her personality. She has been gradually loosening her platform style, leavening her fact-filled lectures on economics, national defense or the law with effective and even humorous ad libs.

She has been trying to make personal contact with as many voters as possible, plunging into crowds and seeking out bystanders she spots in the distance, and often winning them over with a somewhat surprising personal warmth.

Party workers, shoppers, factory employes, farm hands and hospital patients all have been impressed by the way Thatcher was able to talk earnestly and almost intimately with them in the center of a swirling crowd, fixing their eyes with hers.

She impressed workers, even if eventually she bored even the photographers and television crews by trying a hand at one job after another - sewing uniforms in a clothing factory in the red brick textile town of Leicester, packing candy on the assembly line at the huge Cadbury chocolate factory just outside Birmingham and caring for a 12-hour-old calf on a farm in East Anglia.

She has become a master of the media event, ordering reporters out of the background of a good television picture and always giving photographers the opportunity for one more shot, even if it means holding a new-born calf in her arms for a good five minutes.

"Come on," Come on," she finally instructed, "get on with it. This is heavier than your cameras."

She manages to have the best of both worlds on the issue of being woman. She gives interviews about homemaking and her diet, makeup and wardrobe - these days it's mostly tailored suits in various shades of blue, the Conservative Party color, with blouses with ruffles or bows.

She exerts the same kind of strong, personal control over every detail of her campaign that she is expected to bring to the job of prime minister if the Conservatives take control of Parliament.

In press conferences, she instructs members of her shadow Cabinet in her school mistress style when and how to answer questions about details of the party's policies. She frequently prompts reporters when they have left someone out or some question unasked.

Born above her family's grocery store in northeast England, she frequently helped out in the store until going to Oxford University, where she studied chemistry and became president of the Conservative Union. After graduation, she worked as a research chemist and studied law at night.

At 24, she became the youngest woman Tory candidate in the country, unsuccessfully contesting elections in 1950 and 1951 in a strong Labor district. In 1951, she married Denis Thatcher, a tall, thin, ramrod straight man a decade her senior who had inherited a thriving small business that he later sold to the Burmah oil company, retiring from business altogether three years ago.

In 1953, she passed her intermediate law exams in May, bore her children - boy and girl twins - in August, and passed her law finals in December. After working several years as a tax lawyer, she ran again for Parliament in 1959 in the suburban north London district of Finchley, and won at age 34.

She was education secretary in the Conservative government of the early 1970s.Although she was vilified by opponents for ending the free milk program in secondary schools during government-wide budget cutting, she expanded a school construction program, kept the open university alive, and increased government grants for students.

Her close associate in that Cabinet, Health Secretary Keith Joseph also fought for more spending for social services and added an expensive new layer of bureaucracy to the National Health Service.

After the Conservatives were voted out of office in 1974, Thatcher sensed that the party was ready to move to the right. Thatcher and Joseph publicly repented the error of the Health government's ways, something she continues to do during this campaign.

When Joseph, a brilliant but idiosyncratic man, who became the party's leading right-wing ideologist, declined to oppose Heath for party leader in 1975, Thatcher decided to try herself.

With Joseph, she became a convert to the teachings of conservative economists Milton Freidman and F. A. Hayek, deciding that Britain needed less government involvement in the economy, lower taxes to increase individual initiative and business investment, less legal power for labor unions to force acceptance of high wage demands and less money flowing through the economy.

She believes so strongly in this last concept - monetarism - that she tries to explain it like a schoolroom lesson to voters at campaign meetings: "You have got to see that the amount of money put into the country does not exceed the total value of goods and services produced."

She also believes strongly in unfettered private competition.

"Who brought down the cost of air fares?" she asked at a rally. "It was Freddie Laker and private enterprise, not goverment-owned British airways."