Prime Minister Margaret Thatcher, who will meet here with high-ranking Soviet Politburo member Mikhail Gorbachev later this month, said today she has "no doubt" that upcoming U.S.-Soviet arms control talks will be conducted by Washington "on a basis on which there are no concessions unless they are mirrored by equal concessions from the other side on a one-for-one basis."

The British Conservative leader lent her strong support to that approach, declaring, "That is the basis on which we are likely to get the reductions that will hold."

In a wide-ranging interview with American correspondents here, Thatcher credited as "things which bring disarmament talks nearer" the big increases in U.S. defense spending in recent years, and the "great moment of decision when the West stood firmly together and did not in any way submit to the false blandishments of the Soviet Union" not to deploy cruise and Pershing II missiles in Western Europe.

Thatcher said the Reagan administration now has "a historic opportunity and is taking it" and that the western alliance is going into the new year "absolutely firm and with a positive, and agreed, position on East-West relations."

Thatcher's year-end meeting with the U.S. reporters came after a one-hour meeting with U.S. Secretary of Defense Caspar W. Weinberger, who stopped here after a NATO meeting in Brussels and talks in Saudi Arabia.

Asked if, based on her talks with Weinberger, a new Middle East peace initiative by the United States was likely in 1985, Thatcher said, "I believe there probably will be." But she added, "It's easier to say that than to work out precisely what it will be." She said she thought King Hussein of Jordan "would be prepared to play an active role under certain circumstances" in which "he has to keep the Arab world together."

Thatcher will have a busy pre-Christmas week. After meeting Gorbachev on Dec. 17, she will fly to Peking to meet with Chinese Premier Zhao Ziyang and sign the agreement turning over Hong Kong to China in 1997. On her way back, she will stop at Camp David to meet with President Reagan on Dec. 22. She will provide Reagan with a personal report on Gorbachev, who is seen in the West as a possible successor to Soviet President Konstantin Chernenko.

British officials say that Thatcher is, in fact, feeling good about the state of the alliance these days, that Reagan is viewed here increasingly as a pragmatist, and that the prospect of renewed Soviet-American arms talks always lowers the political tensions in allied governments, all of which have domestic headaches to deal with.

The officials said Weinberger's speech last week laying out cautious guidelines for the use of U.S. military force was well received here. Similarly, there is a sense of security that Secretary of State George P. Shultz and White House national security adviser Robert C. McFarlane appear to be the key players in arms control policy.

Nevertheless, officials say, contrary to Thatcher's remarks about agreed positions, there is still uncertainty here about Pentagon-State Department splits on arms policy and about what the U.S. position will be in future arms talks. Shultz will stop here this weekend, and officials are hoping that he will disclose how he will approach his meeting next month in Geneva with Soviet Foreign Minister Andrei Gromyko, which is meant to plan a resumption of actual negotiations.

Thatcher also made the following points:

* Although an increasing number of British politicians of all parties are worried about the increasing, $11 billion cost of Britain's plan to build four Trident missile submarines, Thatcher said the project was "absolutely vital" to maintain the country's deterrence against nuclear attack. But, questioned about ways to trim the program, Thatcher twice mentioned that "the number of missiles you put in is still a matter of consideration."

* Aside from thus far unsuccessful attempts to restore normal relations with Argentina after the 1982 Falkland Islands war, Thatcher has no plans to discuss the islands' sovereignty with Buenos Aires. "The Falklands are British territory. The people have a right of self-determination, therefore their wishes are paramount," she said.

* On Britain's coal strike, which will enter its 10th month next week, Thatcher said, "I don't know how it will end" other than perhaps by the "gradual trickle back to work" of the strikers that has been going on. "It cannot be a negotiated settlement while the leadership of the National Union of Mineworkers holds to a position from which it has never budged: that uneconomic pits can never close. That just doesn't make sense."

When a reporter suggested that the strike was tearing Britain apart and that she may have a vested interest in a more personal effort to settle it, Thatcher said, "Politicians are not there to run industries." That, she said, is up to the state-run National Coal Board.

Thatcher also paid homage to the "enterprise culture of the United States. We had it," she said of Britain, and now "we are trying to regain it." British skills in research and innovation, she said, "are extremely high. But what we are not so good at is turning that into industrial profit. You pick them up, and so has Japan."

What Britain needs to create more jobs and deal with 13 percent unemployment, she said, is to "regain the spirit of enterprise which leads people to say, 'I'm going to start up on my own to build a business that employs people and gives them a living.' You don't hear people in this country saying that enough."