Two new members to join EC?

European Community leaders will meet for a two-day summit in Dublin beginning Monday in a last-ditch attempt to decide on the terms of entry for Spain and Portugal.

The delicate and technical problems that have dragged on for several years were referred to the summit meeting following the failure of EC foreign ministers to agree among themselves here this week on what to offer Spain and Portugal in key areas.

A failure in Dublin could not only jeopardize the timetable for entry of Spain into the EC by Jan. 1, 1986, but it could also turn Spanish opinion against that country's membership in NATO. A controversial referendum on NATO is scheduled for roughly the same time as the EC summit.

In order to try to avoid failure at the Dublin summit he will host, Irish Prime Minister Garret FitzGerald quickly began a tour of EC capitals in quest of a compromise on such problems as fishing and wine production. One Irish official at this week's Brussels meetings remarked that ''there's a basic agreement on everything but wine.'' A senior official of the EC's executive commission said he was optimistic that a solution could be found in Dublin.

Many see continued Spanish membership in NATO as unofficially but inextricably linked to a successful conclusion of the EC membership negotiations and Spain's entry into the EC by the time of the NATO referendum.

Spanish Prime Minister Felipe Gonzalez, in announcing the NATO referendum recently, said he favored continued NATO membership. But public opinion is said to be running against and many see a successful conclusion to the EC talks as the only way for him to rally support for NATO.

The Spanish request for entry into the EC and NATO, sought immediately after the death of dictator Francisco Franco five years ago as a means of solidifying Spanish democracy, has run into several difficulties. France and Italy, although politically supportive, have sought tough terms of entry into the EC for competing Spanish wine, agricultural products, and fishing fleets. It was primarily the wine and fishing terms that the EC ministers had the most trouble dealing with this week. Summit leaders will try to resolve these last remaining problems.

All parties in the EC and Spain and Portugal had sought to have the negotiations over with by late this year. They favor quick action in order to begin ratification of the outcome by national parliaments to meet their joint pledge to enlarge the EC to 12 members by January 1986. While the talks with smaller Portugal have been less controversial, those involving Spain's much larger economic and farm production have been laden with friction.