NATO, East Bloc Start New Round. Western nations take a conservative tack while Moscow talks vague, sweeping change. CONVENTIONAL ARMS TALKS

NATO is struggling to stop looking like the old fogy of conventional arms control. A new round of talks aimed at reducing conventional forces in Europe begins this week. As it opens, the United States and its NATO allies are presenting what critics call a minimalist opening position, while the Soviet Union continues to make vague yet enticing calls for sweeping change.

Taking aim at this perception, British Foreign Minister Geoffrey Howe took care to emphasize the more dramatic aspects of the NATO plan when he outlined it Monday in Vienna. And he said that the new talks ``must not become a competition for who can put forward the more radical proposals. They are a serious quest for stability and security, and not a competitive striptease.''

The NATO proposal is an intricate formula that would limit both sides to 20,000 tanks, 16,500 artillery pieces, and 28,000 armored personnel carriers in Europe. The levels proposed equal 90 to 95 percent of NATO's own current strength.

The NATO formula would also prohibit any nation of either alliance from stationing more than 3,200 tanks, 1,700 artillery pieces, or 6,000 armored personnel carriers outside its own national borders.

The most dramatic aspect of this plan is what it would require the nations of the Warsaw Pact to do, as they have many more of these heavy weapons than does the West. The proposal would require the Soviet Union, in particular, to make large cuts, reducing by two-thirds its tanks and artillery now deployed outside its boundaries in Eastern Europe.

``The Soviet Union will still have more tanks within the area than the United States and West Germany combined,'' Foreign Minister Howe said.

Last December, Soviet leader Mikhail Gorbachev announced a unilateral withdrawal of six tank divisions, among other reductions, in the next two years. Even after this reduction is completed, further cuts would be necessary for the Soviet Union to fit under the proposed NATO ceiling.

The least dramatic aspect of the NATO plan is what it would have the US and its allies to do. With proposed reductions of only 5 to 10 percent in the covered weapons ``we get no budgetary benefits or public applause,'' says Jack Mendelsohn, deputy director of the Arms Control Association, ``though it's maybe not a bad opening position.''

Asymmetric cuts have long been part of the West's approach to conventional arms reduction. A recent, widely quoted Rand Corporation study estimates that conventional weapons cuts have to be skewed 5 to 1 in favor of NATO, if the alliance's position in Europe is not to deteriorate.

But some US analysts claim that with the current improvement in East-West relations bolder action is now called for, for several reasons:

NATO could give up more and still come out ahead. According to a study produced by Barry Blechman, president of Defense Forecasts Inc., a 3-to-1 Warsaw Pact to NATO ratio of reductions would still result in a stable military situation in Europe.

The key, according to Mr. Blechman, is geography. Warsaw Pact reductions have to focus on Northern Central Europe, where NATO is weakest.

``It's possible to make big reductions safely. You've just got to be careful where the units come from,'' Blechman says.

NATO is losing the vision race. Mr. Gorbachev, by talking of a ``common European house,'' making unilateral force reductions, and proposing sweeping cuts of up to half a million troops per side is presenting Westerners with an attractive package deal. Pressures for unilateral defense-budget reductions could well increase in NATO nations.

``The NATO alliance needs something to match Gorbachev,'' says Stanley Sloan, a senior specialist in security policy with the Congressional Research Service.

Mr. Sloan proposes a three-part approach. The first step would involve a proposal of cooperative monitoring measures - an exchange of military inspectors and the like. The second step would be initial force-reduction goals similar to those that NATO is now seeking. The third stage would be an articulation of some broad long-term goal, perhaps a reduction of forces down to 50 percent of current NATO levels.

``Such an approach would hold open the prospect of revolutionary change in East-West military relations while building such change on a cautiously incremental process,'' Sloan writes in a just-published report.

Sloan and other critics say that in recent months NATO has been taking a green-eyeshade approach to conventional arms talks, insisting on what the talks will not cover, such as tactical aircraft and naval forces, while Gorbachev has been indulging in sweeping rhetoric and appealing gestures. While an insistence on stability is of course laudable, ``an insistence on stability as the foremost objective guarantees a losing hand,'' Blechman says.

In the face of NATO conservatism, the burden-sharing debate, in which some members of the US Congress say the US carries too much of the Western defense burden, may get worse. Already this year Rep. Andy Ireland (R) of Florida and Rep. Patricia Schroeder (D) of Colorado have introduced a bill calling for unilateral withdrawal of some 14,000 US troops now in Europe.

But arms control talks are a long and difficult process, and with the conventional talks in Vienna just beginning, there could be a great ebb and flow in public support and interest, as well as changes in NATO policy, one Pentagon official says.

``Now these are just get-acquainted meetings,'' he adds.