President Reagan and West German Chancellor Helmut Schmidt agreed yesterday to give "equal weight" to bolstering missile power in Europe and seeking negotiations with Moscow to mutually limit such arms.

Later in the day, Secretary of State Alexander M. Haig Jr. told a news conference that during his recent discussions with Soviet Ambassador Anatoliy Dobrynin Moscow appeared "ready and willing" to participate in those negotiations by the end of this year. This was the first public indication from the United States that the Soviets were prepared to talk on this issue.

Assurances that the United States is committed to both courses of action are important to Schmidt at home. The chancellor faces increasing opposition from the left wing of his own party and others who don't want new U.S.-built missiles in West Germany and don't believe the new Reagan administration is sincere in saying it will attempt to negotiate eventual curbs with Moscow. Those curbs are also meant to limit Soviet weapons already in place.

Schmidt ended his first two-day summit meeting with Reagan yesterday saying he was "deeply satisfied" with the discussions, and with the president talking of establishing a friendship and relationship with Schmidt "that bodes very well for the future and for the West."

During a subsequent speech and question-and-answer session at the National Press Club, however, some differences of opinion on trade and financial strategy and perhaps on Middle East policy were evident.

Asked aobut the recent U.S. move to limit imports of Japanese cars, Schmidt at first said he would not comment but then said he was "not happy about it." West Germany relies heavily on free foreign trade and Schmidt said such restrictive measures may become "contagious." Protectionist measures brought about by pressure groups are "very easy to get into but very difficult to get out of," he said.

On economic matters, the chancellor, who has sometimes been criticized for lecturing his partners, said he didn't come here to give "lectures or lessons." But "the only thing I want to be understood in Washington," he said, "is that a long period of interest rates at 20 percent [in the United States] inevitably spreads to other countries and for us in Europe this is too high."

The Europeans fear these rates fuel recession in their own countries and, though Reagan said he was "keenly aware" of the European concerns, Schmidt did not forecast any quick solution and predicted that interest rates will be as important a topic as energy at the next seven-nation Western economic summit in Ottawa in July.

On the Middle East, Schmidt backed the Carter administration's Camp David agreement between Israel and Egypt as a step toward peace.But he warned that Arab countries fear that without a far more comprehensive political solution in the region, the Soviets will have more opportunity to interfere.

In contrast to the administration's effort to have the Arabs focus on Moscow as the immediate threat, Schmidt said "the Arab leaders and I share the view that the more the West alienates the Palestinians, the more will they be drawn towards the Soviet Union."

Schmidt also sought to put into perspective recent expressions here that Europe and West Germany were becoming neutral or pacifist.

Schmidt told the press club audience that naturally there are opposition movements in all countries, and Haig added later that there are such groups here, too, opposed to the MX missile, for example.

But the key thing, he said, is that "public opinion in Europe expects every possible step to be taken to stop the uncontrolled growth of nuclear weaponry, the dangers of which, if only for geographical reasons, are very real to us in the Federal Republic of Germany."

The deployment of additional nuclear-tipped missiles in a densely populated region "roughly comparable to the area between Boston and Washington was not a decision to be taken lightly," he said.

What governments must do, Schmidt said, is convince people that this is not an unlimited arms race, that the Soviets started it, and that the West is genuinely willing to negotiate mutual cutbacks. "The majority of my people are convinced," Schmidt maintained, and "so far, I have no doubt" about parliamentary support either.

Schmidt noted that Bonn's 500,000-man armed forces still rely on a draft and that, too, sometimes contributes to public disgruntlement over defense issues.

The chancellor also said he expected the new socialist government in France of Francois Mitterand to carry on the close post-World War II ties with his country. Schmidt will visit Paris and Mitterand Sunday on his way home from Washington and will carry a message to the new French leader from Reagan.