PARIS, SEPT. 30 -- Vice President Bush assured West German Chancellor Helmut Kohl today that the United States would not "decouple" its nuclear deterrent from Western Europe and he delivered a letter from President Reagan pledging continued efforts to improve superpower relations.

Bush spent less than 24 hours in Bonn as he hopscotched across Western Europe for a series of meetings with allied leaders that are part of the vice president's effort to portray himself as an experienced diplomat. He flew on to Paris tonight for a similar meeting with Prime Minister Jacques Chirac and President Francois Mitterrand.

The vice president appeared before reporters for six "photo opportunities" with various West German officials and what his schedule described as a "brief press encounter and photo opportunity" with Kohl at his side.

The two leaders praised each other, reiterated well-known policies and then took one question, which, as it turned out, was about a subject they said they had not discussed -- international economics.

At an earlier picture-taking session, Bush handed Kohl the letter from Reagan. He is delivering similar letters to all of the allied leaders.

Friedhelm Ost, the West German government spokesman, said the letter informed Kohl that Reagan believes the United States is "on the verge of a qualitative change for the better" in relations with the Soviet Union. Reagan said it is his intention to "continue on this course step by step," Ost said.

The remarks about improved relations come as the superpowers have reached agreement in principle to eliminate medium-range and shorter-range nuclear missiles from Europe. The proposed treaty, which is still being ironed out, generally has been welcomed by the allies, and was discussed today by Bush and Kohl.

Kohl cleared one of the last remaining obstacles to the agreement Aug. 26 when he announced that West Germany would scrap its Pershing IA missiles if the superpowers eliminate their medium-range and shorter-range weapons.

An informed U.S. official said Kohl told Bush the next step should be to negotiate reductions in conventional forces in Europe, in which the Warsaw Pact has a large numerical advantage. A West German government source said Foreign Minister Hans-Dietrich Genscher urged Bush also to move ahead on a treaty to limit chemical weapons.

"We agree on where we should go," Bush said. "There is no danger, in my view, that the United States will use any arms control agreement, or anything whatsoever, to decouple, to move away from our commitment to NATO.

Kohl reassured Bush that while Bonn wants better ties with East Germany, "there is no price we will ever be ready to pay or . . . would be ready to accept which would divide us from our friends. . . . We do not wander between two worlds. We are part of the free world."