LONDON — HOW large should the European Community - already a powerful grouping of 12 member-nations and a total population of 340 million - be allowed to become? The question is fueling a growing debate as a list of applicants to join the EC continues to lengthen, and nonmembers in East and West Europe eye the advantages of joining what until now has been an exclusive ``Euro-club.''
The latest nation to knock on the EC's door is the small Mediterranean island of Malta (population 350,000). On July 16, it followed Cyprus, Austria, and Turkey in lodging a formal membership bid.
In doing so, it sharpened what for Jacques Delors, president of the Brussels-based European Commission (the EC's executive arm), was already a political dilemma.
``Mr. Delors,'' a Commission official said last week, ``has to try to reconcile two imperatives that are currently gathering momentum: a wish by existing EC members to deepen their relationship before new members are admitted, and the desire of countries to join as early as possible.''
The official said the line of EC aspirants was likely to grow in the next few years - but Delors held out little hope that a ``yes'' answer would be given to any but one or two of the applicants in the foreseeable future.
That view seems bound to become increasingly controversial as countries in Europe's two halves continue to adjust to the fading of the cold war and as the advantages of EC membership become more compelling.
William Wallace, deputy director of the Royal Institute of International Affairs here, and author of a new study, ``The Transformation of Western Europe,'' called the Delors's view ``understandable but unsustainable.''
``Admittedly, there is a lot of work to be done before the European single market comes into being in 1992, but after that happens, the EC is going to expand well beyond 15 nations in the next 10 years.
``I can envisage a Community of 20 or more nations, with a total population of over 400 million. The pressures will be too great for anyone to hold out against qualified nations determined to enter,'' Dr. Wallace said.
There is certainly evidence of a head of steam building up for a wider EC. In Scandinavia and Switzerland, there is quickening discussion of the issue. And Europe's former communist states are beginning to position themselves for EC membership in the next few years.
For example, on July 17 Jozef Antall, the Hungarian prime minister, said: ``Our strategic aim is to obtain EC membership by 1995 - after Austria, no doubt, but before all the other countries of what used to be called Eastern Europe.''
In January 1989, Delors, foreseeing a pileup of membership applications, tried to create a political buffer against at least some of them. He told the European Parliament in Strasbourg, France, that the 12 EC countries, plus the members of the European Free Trade Association (EFTA - Finland, Iceland, Norway, Sweden, Switzerland, and Austria) should enter a dialogue aimed at the creation of a ``European Economic Space'' (EES) which, starting in early 1993, could act as an 18-nation free trade zone.
Since then, however, political contacts between the EC and EFTA, aimed at producing the expanded grouping, have been going badly.
When the EFTA partners at a meeting in Gotenburg, Sweden, issued a statement on June 14 saying they would join the proposed zone only if they were given a seat at the top table in Brussels, Delors began backing away from his original proposal.
``We are not going to throw away the achievements of 30 years for a gamble that is not worth it,'' he said.
The tone of his remarks appeared to suggest that, in proposing the EES, Delors's real motive was to try to deflect the enthusiasm of the EFTA nations and any other country eager to join the EC or forge a close relationship with it.
An Austrian diplomat said: ``Our impression is that he is merely buying time, and that is very discouraging. If the current contacts between the EC and EFTA get nowhere, which now seems likely, our partners in EFTA may have to join Austria in thinking in terms of straightforward applications to join the EC.''
Wallace concurs. If the EC-EFTA talks fail to produce an agreement, he said, ``there may be no alternative but for them to seek full EC membership. It would be extremely difficult to turn them down if they pressed hard.''
In June, Delors's discouraging remarks roused Douglas Hurd, the British foreign secretary, to call for a more open-minded approach to new applications. Mr. Hurd in June said: ``It will be at least 1993 before new applications can be entertained. But after that I do not see how the Europe of the 12 can shut the door for any length of time against fully qualified European democracies which are anxious to join, whether they are now in EFTA or in Central Europe.''
Inside the Berlaymont building, headquarters of the EC, Hurd's remarks provoked concern. The reaction, which was believed to reflect Delors's thinking, suggested that a clash will eventually occur between the Commission, determined to deepen the EC before it gains extra members, and those who would like to see the EC expand anyway.
Pascal Lamy, one of Delors's top officials, said that early and rapid expansion of the EC beyond the present membership would run the risk of ``diluting'' the Community and make it harder to take decisions.
Mr. Lamy said the EC might be able to expand its membership by another ``two or three'' members, ``but not beyond.'' If membership went over 15, he said, the Community would become ``unwieldy and diffuse.''
Such views are also strongly held in the European Parliament. Lord Nicholas Bethell, a British member of the European Parliament (Euro-MP), said: ``We may be able to accommodate Austria if it abandons its present neutral status in world affairs, but otherwise I do not see more than one or two members being added to the EC in the next 10 years.''
Lord Bethell said he believed his view was shared by ``a majority of Euro-MPs.''
Lord Bethell noted that there has been growing resistance to Turkey being admitted to the EC, and that the application of Cyprus was likely to run into trouble because the island remains divided between Greek and Turkish communities.
Even if East European countries are excluded for a while on the grounds that they are not yet mature democracies, as the Treaty of Rome (the EC's constitution) requires, Delors and his officials seem certain to come under heavy pressure to change their restrictive view of membership.
Public opinion in Scandinavia, where Denmark is already a member of the EC, indicates that more countries would like to line up on Delors's doorstep than he believes the EC can cope with.
In Norway, which in a referendum decided 18 years ago not to join the EC, an opinion poll earlier this year indicated that more Norwegians now favor membership in the EC than oppose it.
Finland, whose constitution requires it to be nonaligned, is also showing signs of a rethink. Last May, a Gallup poll suggested that 60 percent of Finns favored EC membership. And in Sweden, argument is raging on future relations with the EC as well.
If William Wallace is right in believing that Delors will be unable able to prevent the EFTA countries and others from joining the EC, the prospect of a grouping of as many as 18 or 20 countries becomes thinkable.
``It can easily be forgotten that the EC started with six members, and has since added as many again,'' he said.