EC's glow of success dimmed by reminder of much work ahead

''Yes, we're going to have a European flag, a European anthem, and even a European honors list,' French President Francois Mitterrand said. The French leader smiled and laughed. He was talking to journalists after heading a two-day Common Market summit here that succeeded in resolving the British argument over its budget payment, and his euphoria over the major diplomatic triumph was barely containable.

But Mr. Mitterrand's joyous chuckle also had a nervous tone to it, as though he knew the tour of his European dream world was a bit far-fetched. Indeed, the glow of success, though strong, was being somewhat dimmed Wednesday by an undercurrent of haggling and the knowledge that much work remains to be done for the European ideal to be achieved.

The first letdown concerned money. While the agreement removed the main obstacle to balancing Community finances in the future, it failed to address the immediate problem of this year's expected $1.8 billion shortfall. Foreign ministers will have to meet soon to solve this issue.

Moreover, commentaries around the Continent were not so exultant as might have been expected. Preoccupied by the resignation of Economics Minister Otto G. Lambsdorff, German commentators largely ignored the larger European question. French observers generally saluted the agreements in big headlines, but they also raised doubts.

The doubters claimed Mitterrand had given too much away to his British adversary in order to gain his diplomatic success. Who would pay for the Community now that Germany's payments were limited and the British contribution cut? asked the conservative daily Le Quotidien. French taxpayers, of course, the paper said.

The criticism was strongest in Britain. The prime minister will face tough questioning in Parliament this week. The Labour opposition sniped that she had sold out. And even pro-Conservative papers such as The Times described the agreement as temporary, ''a cease-fire.'' Britain's rebate deal, the critics feared, would be good only until the EC needed to raise taxes again.

''There is no guarantee that the war will not break out again in three or four years' time,'' The Times wrote. ''More money will require more negotiations.''

Foreign Minister Geoffrey Howe disputed this claim in conversations after the summit. He stressed the principle of tying a country's contribution to its wealth was now generally accepted. ''Britain could veto any change in the system ,'' he added, explaining that ''any further negotiations would give us more money.''

For his own domestic reasons, Mitterrand stressed just the opposite in his talks with journalists. He said the agreement is ''limited in time'' and the increase in French contributions would be limited.

But the French leader - and the other heads of state - emphasized the path was mostly cleared for ''the construction of Europe.'' The first objective is to complete negotiations for Spanish and Portuguese membership.

Beyond this, the Europeans will begin to focus on other goals, such as an end to frontier impediments to trade, wider integration of education systems, and an increase in Community funding to existing and new projects. Mitterrand announced that a working group had been set up to study these questions and all other proposals designed to develop a European identity.

''The list is too long for me to read it to you,'' Mitterrand said. Then he chuckled, half in triumph, half in recognition that it probably will prove too long for the Europeans to agree on.