West German Chancellor Helmut Kohl, concerned about his image at home and abroad, is hoping to use this week's gathering of world leaders in New York marking the United Nations' 40th anniversary to boost his sagging stature.

Kohl will arrive in New York Tuesday to conduct two highly publicized encounters with President Reagan and separate meetings with the leaders of India, China and Israel on the fringe of U.N. festivities.

According to U.S. officials, Kohl in effect "invited himself" to consult with Reagan before next month's U.S.-Soviet summit meeting in Geneva, in an awkward attempt to demonstrate that West German interests were being taken into account.

The White House, evidently worried that other allied leaders would feel overlooked, proposed in return this Thursday's session that will group Reagan with government leaders from six leading industrial countries. France spurned the offer, but West Germany, Italy, Canada, Japan and Britain have agreed to participate.

Kohl, however, still persisted in seeking a private session with Reagan, which he was reluctantly granted. The other leaders attending the presummit consultation also will receive personal audiences with Reagan in New York.

"We really don't know why Kohl was so adamant about seeing Reagan or if he has anything important to say," said an American involved in planning the consultations. "He is usually extremely shy around Reagan and probably just wants to show that the president will listen to him."

Once regarded as a primary bridge between East and West, Bonn has lost much of its earlier influence over political and diplomatic contacts between Moscow and Washington since Kohl assumed power three years ago.

Mikhail Gorbachev's decision to travel to Paris this month on his first official visit to the West as Soviet leader was seen as a telling comment on the chancellery's reduced clout since the days when Konrad Adenauer, Willy Brandt and Helmut Schmidt were considered important intermediaries between Soviet and American leaders.

Kohl has tried to compensate for his government's diminished dialogue with the Soviet Union by emphasizing his close personal ties with Reagan. But lingering resentment at the White House over the anguish and embarrassment caused to Reagan by the Bitburg ceremony in May has impaired faith in Kohl's judgment, U.S. officials said. At Bitburg, the chancellor insisted that both leaders honor German war dead at a cemetery containing SS graves,

The vacuum in Bonn's statesmanship has been filled largely by President Richard von Weizsaecker, who has earned high praise from all political parties for his forthright yet sensitive interpretation of West Germany's delicate relations with Israel and Eastern Europe.

The West German president recently concluded a highly successful visit to Israel, where his warm welcome was attributed by many observers to his eloquent speech on May 8, the 40th anniversary of the end of World War II, in which he acknowledged the need for every German to confront the nation's guilt over the Holocaust.

Von Weizsaecker, a senior member of Kohl's Christian Democratic Union, is known to harbor a strong dislike for the chancellor's heavy-handed political style and his claim of pursuing "moral and spiritual renewal" even though his center-right government has been buffeted by various scandals.

Von Weizsaecker's popularity is considered a key factor in preserving the political strength of the Christian Democrats even while Kohl's standing in public opinion polls has dropped steadily.

In contrast with his Social Democratic predecessor Helmut Schmidt, who remained the country's most respected politician even as his ruling coalition disintegrated and voters abandoned his party as it drifted to the left, Kohl has become increasingly viewed as an electoral liability by fellow Christian Democrats as they approach the 1987 national elections.

Christian Democratic strategists, while confident of victory in the election 15 months away and a continuation of the ruling coalition with the Free Democrats and Christian Social Union, concede that their party may not score as well as in the 1983 vote because of widespread disenchantment with Kohl's leadership qualities.