The long-delayed visit of Soviet President Leonid Brezhnev to West Germanny begins today, with intensive Western interest focused on the ailing health of the Soviet chief and on his attitudes toward the ailing state of East-West detente.

Although Bonn and Moscow have many long-standing issues on their agenda, including trade and the security of West Berlin, Brezhnev's decision to visit here now - nearly four years after Bonns invitation - has given this trip potentially far wider political significance.

The 71-year-old Soviet leader comes here just before two key meetings of the North Atlantic alliance in Brussels and Washington and a special session on disarmament of the United Nations in New York.

Perhaps more importantly, he comes during a period in which both Soviet and West German relations with the Carter administration have deteriorated and while some confusion lingers within the Western alliance about U.S. defense, economic and nuclear export policies.

This had led to some concern, as it did last summer when Brezhnev visited Paris, that the Soviets may be trying to take advantage of the situation and drive a wedge between the United States and its NATO partners, expecially West Germany - the most economically and militarily, powerful state in Western Europe.

The confusion in the alliance gives Brezhnev the maximum potential for disturbance," the respected Swiss newspaper Neue Zuercher Zeitung cautioned this week, "by showering the Western public with protestations of peace and creating doubt about the need for intensified defense efforts, while the Soviet arms machinery is in full swing."

Yet the Soviets, as one top West Germany official put it, "are not dreamers. They know it is not possible to split the U.S. and West Germany, and if they tried openly it would be counter productive.

"Therefore they will be very careful.

But it is always in the back of their mind. As far as Europe is concerned, it is certainly in Moscow's interest to try to decouple it from the U.S. to loosen the alliance.

"That is their idea of where East-West detente should lead," he adds, "so you cannot exclude the possibility for some mischief if the opportunity arises."

Brezhnev was last here in 1973, when Willy Brandt was chancellor and after Bonn and Moscow had concluded a major round of dramatic contacts and treaties that formed the cornerstone of Brandt's efforts to reach out to Eastern Europe and heal the wounds of World War II.

As Brezhnev begins his four days of talks here with Chancellor Helmut Schmidt and other top official, however, the Soviet leader is clearly in poor health. Among West experts, the view is that Brezhnev, as one put it, "is no longer in absolute command," that Soviet leadership is "in a period of transition with at least some measure of collective leadership."

Some specialists feel the visit, putting aside diplomatic and economic reason, "is very much a matter of health."

In this view, the visit is meant to portary a healthy Brezhnev, still in command, able to carry out face-to-face diplomacy and travel. It is a message presumable meant for both the White House and the Soviet Politburo.

Furthermore, the trip here has been put off so often, that specialists here surmise that the Soviet leader may feel this was the last chance, before the end of the Brezhnev era, to shore up the policy towards the West that he agreed to and that has always had some critics within the Soviet heirarchy.

Perhaps Brezhnev's biggest gamble was to allow a growing Soviet economic dependance on Western, and especially West German, industrial techonology and credit.

Nevertheless, Brezhnev's image as a healthy man has already been blurred by changes in his schedule here that are designed to relieve the strain on him.

A visit to the Ruhr industrial area has been dropped as have meetings with several industrialist. A proposed press conference now is likely only to be statement to the press. "They are simply letting as few people as possible see him up close," one diplomat said, while cautioning that Brezhnev is unpredictable and may change plan on the spot.

In comparison to the burst of treaties that normalized relations between Bonn and Moscow in the early 1970s diplomatic relations between the two leading European powers have been generally stagnat in recent years. Futher agreements initiated in 1973 on culturalm scientific and legal issues have never been rarified due to a continuing dispute over West German demands that they should also cover West Berlin.

Trade, however, has been booming. Last year, total trade totaled some $5 billion and West Germany is now Moscow's biggest trading partner in the West.

West German exports to the Soviet Union, however, dominate that trade and the Soviets, saddled with huge debts to the West, are trying to cut their deficits and place more emphasis on "barter deals" rather than paying with more Western credit.

West German industrial leader Otto Wolff von Amerongen this week cautioned that there are limits to such compensation deals and suggested increased Soviet deliveries of oil and uranium as possible future offsets.

The prospect of West Germany purchases or uranium from the Soviets or of using Soviet enriched uranium processing facilities, although not now contemplated by Schmidt's government, is nevertheless seen in Europe as one possible counter to new U.S. nuclear export laws.

Although no major new diplomatic agreements are expected to be signed here, a new long-term economic cooperation plan will be signed which officials believe will help Brezhnev to bolster his case at home.

Although both the Soviet and West Germans have placed emphasis on this visit as a step towards improving the troubled status of detente the Soviets have put special emphasis on the economic aspects. The Soviet press has desribed the visit as the event of the year.

The West Germans, however, will stress the need for more positive Soviet steps in the disarmament field, especially after President Carter's decision to defer production of neutron weapons.

Schmidt is concerned over the Soviet arms buil-up and also over Bonn's stagnant relations with East Germany, which is under Soviet Political domination.

Thus, a successful "Brezhnev visit here could open the way for a Schmidt meeting with East German Communist chief Erich Honecker this fall and for easing tensions between the divided Germanys.

There are also still almost 2 million ethnic Germans in the Soviet Union and another million scattered elsewhere in Eastern Europe. Bonn would like to get back those who want to come, and keep open the gates to travel.