BONN, FEB. 26 -- West Germany, seeking to postpone plans to modernize European-based nuclear arms, is balking at such a commitment until the western allies can decide what nuclear weapons are needed to ensure deterrence through the next decade.

Chancellor Helmut Kohl told parliament yesterday that any decision to replace older nuclear weapons with modern, upgraded versions should be made only after the North Atlantic Treaty Organization concludes a review of its security policy and develops a "comprehensive concept" for allied nuclear forces in Western Europe.

Kohl said he hoped that next week's NATO summit would give "important impetus" to the study, which the Bonn government complains has progressed too slowly.

Bonn's position has emerged from a complicated debate both within NATO and Kohl's governing coalition on how to adjust alliance nuclear strategy following the signing in December of the Intermediate-range Nuclear Forces (INF) treaty by the United States and the Soviet Union.

The INF treaty will eliminate all U.S. and Soviet ground-based nuclear missiles with ranges of between 300 and 3,500 miles. NATO is studying how to ensure a nuclear deterrent with what is left: ground-based weapons with ranges of less than 300 miles, and air- and sea-based systems.

The West Germans would like reliance on short-range, or tactical, nuclear weapons to be curtailed as much as possible because the arms most likely would be used in their country, which lies at the center of a potential East-West battleground.

But most of West Germany's allies, especially Britain and France, want to delay as long as possible any negotiations on reducing short-range weapons. They fear that enthusiasm for disarmament in Europe, and especially in West Germany, inevitably would lead to an agreement to do away with such weapons and weaken NATO's nuclear deterrent.

In the NATO review, which some officials expect to last until 1990, the Germans want the alliance to decide what numbers and types of nuclear weapons are the minimum necessary in Europe to deter a Warsaw Pact attack, West German officals said. This would establish a bottom limit on how far NATO can go in future disarmament negotiations.

In addition, the West Germans hope to use this process to make what in effect would be a tradeoff with their allies on NATO strategy. The Bonn government would like NATO to agree on reductions in arsenals of short-range nuclear weapons in exchange for a West German pledge to support modernization of whatever weapons remain.

Volker Ruehe, a top-ranking security expert in Kohl's Christian Democratic Union, suggested in an interview that the total number of NATO's nuclear warheads in Europe could be cut in half and still provide an adequate deterrent, if the right types of weapons remained.

That would reduce the number of NATO warheads from 4,000 -- the total remaining in Europe after implementation of the INF treaty -- to 2,000.

NATO's arsenals of nuclear artillery, which have ranges of less than 20 miles, could be cut by 80 percent, Ruehe said.

The issue is not expected to be the subject of significant dispute at the two-day NATO summit, which begins Wednesday in Brussels, according to U.S., West German and British officials.

The summit is likely to reaffirm existing NATO strategy and to issue a declaration providing more details on NATO's objectives in negotiations on reducing conventional forces in Europe, they said.

Kohl said NATO would emphasize the importance of eliminating the Warsaw Pact's perceived superiority in conventional forces.

But the West German position, which has been clarified in recent weeks in preparation for the summit and during Kohl's visit to Washington last week, will be at the center of NATO strategy discussions later in the year.

It is not clear whether the rest of the alliance, particularly Britain, will be content to wait two years before obtaining a firm commitment on modernization. There also is no agreement within NATO on whether modernization should be linked to reductions in short-range weapons.

West Germany is especially interested in postponing a decision on whether to deploy an updated version of the short-range Lance missile, with extended range and improved accuracy. The other principal modernization program under consideration is for development of an air-to-surface missile with a proposed range of 250 miles, which would increase the capability of NATO aircraft to hit Soviet territory with nuclear weapons.

U.S. Defense Secretary Frank C. Carlucci said recently that modernization of NATO's European-based nuclear weapons is essential. But the United States agreed during the Kohl visit that there was no need to press West Germany for specific modernization commitments at this time.

"Our demand, that there may not be any isolated decisions about individual weapons systems, met with full understanding," Kohl said in a formal report to parliament yesterday on his U.S. visit.

"Our alliance must now concentrate on its comprehensive concept of security, disarmament and arms control, and . . . eventual decisions may only be made within this framework," Kohl said.

{The Paris newspaper Le Monde said Friday that French President Francois Mitterrand will tell the NATO summit that the alliance should shelve plans to modernize very short-range nuclear missiles and artillery in West Germany.}

In an important shift in thinking in Bonn, conservatives in Kohl's coalition have become increasingly outspoken about their desire for early negotiations on short-range weapons.

This has aroused fears in Bonn that the existing consensus on the need for a nuclear deterrent could be shattered if West Germany were forced by its allies to commit itself in the near future to modernize such weapons. In this view, conservatives might join an unusual anti-modernization coalition headed by the left-of-center political opposition.

Hans-Jochen Vogel, leader of the opposition Social Democratic Party, said yesterday that it would be better to remove all nuclear weapons from the country than to deploy any new ones.

"It's the wrong moment, for political reasons," to announce modernization plans, a West German official said. The government does not want a political squall over the issue to dampen enthusiasm for the INF treaty, he said.