Bulgaria's ambassador to the United States, Stoyan I. Zhulev, appealed yesterday for improved relations between the two countries, saying his government will respond with an "appropriate contribution" to each sign of interest from Washington.

In a meeting with U.S. reporters, his first in more than four years as envoy here, Zhulev said last week's U.S.-Soviet talks in Geneva and forthcoming arms negotiations "open real opportunities for a positive change in the political climate."

Zhulev's news conference, along with increased embassy activity on Capitol Hill, appeared to reflect a Bulgarian desire to capitalize on the arms talks in expanding ties with the United States, while maintaining its position in the Eastern European bloc dominated by the Soviet Union since 1945. In the past, Bulgaria has been among the bloc countries most closely aligned politically with Moscow.

U.S.-Bulgarian relations have retrogressed in the past several years, Zhulev said, but "certain steps" in the last few months point toward improved relations, he said.

He cited Deputy Foreign Minister Ljubin Gotsev's visit to Washington last October to resume annual diplomatic talks that were suspended in 1981. Another sign of improvement, Zhulev said, was the signing of a two-year cultural exchange agreement last December.

He branded as "groundless" and "lies" charges that the Bulgarian secret service aided Turkish gunman Mehmet Ali Agca in the attempted assassination of Pope John Paul II in 1981. He said that despite "a lot of publicity" there was "no proof and no evidence."

Zhulev said there have been "hints" that the charges about Bulgarian complicity in the papal shooting were behind some adverse developments in U.S. relations, including termination of a Bulgarian-American private economic council and cancellation of the showing of a Bulgarian film that was edited with U.S. cooperation.