U.S. and European negotiators ended three days of talks here yesterday on a variety of key trade issues with both sides generally optimistic that the major nations may be able to agree soon on a worldwide plan for resolving the steel problem.

Viscount Etienne Davignon, steel spokesman for the European Common Market, predicted at a press conference after the talks that "before the end of the month of November, something could be worked out which will be acceptable to all groups."

While U.S. officials were not quite so ebullient, those present at the talks indicated the administration was encouraged by the Europeans' responses to American proposals. Both sides emphasized there were no formal agreements made.

Both Davignon and Withelm Haferkamp, the European Commission's vice president for external affairs, confirmed that Europe was reeptive in principle to a budding White House plan to resolve the steel problem here by effectively establishing minimum prices for imports.

In separate conferences, the two expressed hope that Europeans would be consulted before the U.S. establishes such prices. But, Davignon added, "in some way or another, the price element should be in (order) for any short term crisis solution."

The American proposal, explained to the Europeans this week but not actually laid non the table, would set so-called "reference" prices for steel imports and slap stiff tariffs, or extra duties, on steel products sold here below those benchmark prices.

U.S. officials stressed that the administration still has not decided formally on the plan, which was described as "one of several" items under consideration. However, knowledgeable sources said if some legal problems can be ironed out, the pricing plan seems likely to be adopted.

The European attitude on the steel pricing plan was two-fold.

On the one hand, Common Market officials greeted it as a constructive short-term measure to defuse the steel problem. One key European spokesman termed the plan "a good starting point" for a broader pact.

At the same time, the Europeans were apprehensive lest they not be consulted before the administration sets its "reference" prices, and that the plan might, if carried too far, eliminate all steel imports from specific blocs or groups of countries.

Davignon also suggested, although he did not formally demand, that if the U.S. adopts the minimum-pricing plan American steel makers should in return drop the "dumping" charges they have filed in recent weeks, many of which are against European steel producers.

Dumping refers to the practice by which some foreign producers sell their products here at below their domestic production and transportation costs. The practice is illegal under U.S. and international law, and is punishable by extra duties where a U.S. firm is injured.

The minimum-pricing plan is being worked out by a special administration steel task force headed by Anthony M. Solomon, the undersecretary of the Treasury for monetary affairs.

The group is expected to issue its recommendations in a few weeks - including some proposals for special tax breaks.

There was no immediate indication as to what, if any, agreements the negotiators reached on non-steel issues. However, Haferkamp said the rest of the talks went "constructively" and predicted bargainers would be ready to get world-wide trade negotiations under way by January.

U.S. officials stressed yesterday that the minimum-pricing plan they are considering still has several important problems to be resolved and that the plan is far from final.

Davignon, however, said yesterday he regarded most of these issues as relatively minor. "My impression is," he told reporters late yesterday, "that we are close enough from a technical point of view to be able to avoid a confrontation."