THATCHER: Briton Addresses Congress, Backs ‘Star Wars’ : Thatcher Solidly Backs ‘Star Wars’ : But She Tells Congress That Moscow May Insist on a Restricted Program

British Prime Minister Margaret Thatcher on Wednesday seconded President Reagan’s determination to press ahead with his “Star Wars” research program, although she said the Soviet Union may refuse to limit offensive nuclear arms unless the United States agrees to restrictions on the anti-missile defense effort.

“If we are to maintain deterrence, as we must, it is essential that our research and capacity do not fall behind the work being done by the Soviet Union,” Thatcher said in a speech to a joint session of the House and Senate. “That is why I firmly support President Reagan’s decision to pursue research into defense against ballistic nuclear missiles--the Strategic Defense Initiative,” as the “Star Wars” plan is formally known.

But during a 2 1/2-hour working lunch at the White House, Thatcher and Reagan agreed that the Soviets are likely to try to link offensive weapons talks to their effort to block the Administration’s space missile defense plan when the superpowers resume arms control talks next month in Geneva. A senior State Department official said Thatcher used the phrase “hold hostage” in describing the probable linkage.

Close Ties Stressed

Reagan and Thatcher, making her second visit to the United States in two months, emphasized the close relations between Britain and the United States and their own personal and political friendship. The President called Thatcher “a dear friend and respected leader,” and the prime minister said she could work effectively with Reagan “because we see so many things in the same way.”

Thatcher became the first British prime minister to address a joint session of Congress since Winston S. Churchill appeared before one on Jan. 17, 1952. Her speech, interrupted by applause 24 times and given a standing ovation of almost three minutes at the end, consisted largely of praise of U.S. policy.

But, despite her endorsement of research on anti-missile defense systems, Thatcher drew a distinction between research and deployment. The United States should not attempt to deploy the weapons without first engaging in a new round of negotiations with the Soviet Union, she said.

Also, Thatcher made it clear that she does not share Reagan’s hope that the defense initiative could some day make nuclear weapons obsolete.

‘Intolerable Price’

“Wars are not caused by the buildup of weapons,” Thatcher said. “They are caused when an aggressor believes he can achieve his objectives at an acceptable price. . . . Our task is to see that potential aggressors from whatever quarter understand plainly that the capacity and the resolve of the West would deny them victory in war and that the price they would pay would be intolerable.

“That is the basis of deterrence,” she declared. “It is the same whatever the nature of the weapons. Let us never forget the horrors of conventional wars. . . . Our task is not only to prevent nuclear war but conventional war as well.”

She said that the nuclear balance of terror has kept the peace in Europe for almost 40 years, “one of the longest periods without war in all our history.”

As Thatcher spoke, several hundred Irish-Americans sympathetic to the Irish Republican Army and its efforts to end British control of Northern Ireland, marched outside the Capitol, chanting: “Brits out, peace in.” While ignoring the protesters, the prime minister denounced the IRA and Americans who give it financial or political support.

“The problems of Northern Ireland will not be solved by the assassin’s gun or bomb,” she said. “Be under no illusions about the Provisional IRA. They terrorize their own communities. They are the enemies of democracy--and of freedom, too.”

If a majority of the citizens of Northern Ireland wanted to cut their links to Britain, she said, “I believe that our Parliament would respond accordingly.”

Although the emphasis throughout Thatcher’s brief visit was on agreements between her and Reagan, the prime minister chided the United States for its budget deficit, high interest rates and the soaring value of the dollar, which she said create problems for governments around the world.

“We support strongly your efforts to reduce your budget deficit,” she said to Congress. “No other country in the world can be immune from its effects--such is the influence of the American economy on us all.”

In her talks with Reagan and with other Administration officials, Thatcher called for a gradual decline in the dollar’s value, arguing that a rapid decline would cause almost as many problems for the world economy as the present strength of the U.S. currency, the senior State Department official said.

He said Treasury Secretary James A. Baker III told Thatcher that “recently we’ve been more active in intervention (in currency markets to hold down the dollar value) than any time in the last four years.” But he said Baker noted that there are limits to what the government can do in this area.