As he has done every day for the past nine years, former colonel George Papadopoulos spent today in a high security cell in Athens' forbidding Korydallos prison. Papadopoulos is serving a life term--commuted from a death sentence--as one of the leaders of the repressive military junta that ruled Greece from 1967 to 1974.

But today was an unusual and even festive day for the former dictator. Papadopoulos chose Jan. 29 to launch a new, far right-wing political party, the National Political Union, known by the abbreviation EPEN.

Papadopoulos hopes to use the party to secure his release from jail. His plan is to lead the party ticket in the June elections for the European Parliament, the legislative body of the European Community.

"If Papadopoulos secures a Europarliament seat from prison, then the government will be faced with a serious problem," party spokesman Marios Angelis said.

The former junta leader also hopes his new party will provide right-wing voters in Greece with a dynamic alternative to the governing Socialists, party officials close to Papadopoulos said.

The Socialists took power in Greece from the conservative New Democracy party in 1981.

Since then, analysts agree, New Democracy, the main opposition group, has failed to recover electoral ground, fraught by disorganization and bitter internal quarrels for the leadership.

Shouting, "He is worthy, he is worthy," and bypassing a formal election procedure, an estimated 5,500 supporters gathered outside Athens' central Caravel Hotel this morning approved Papadopoulos as head of the new party.

"No one will contest this decision. Papadopoulos is the spirit of our party," Angelis said.

"Without him, we would be nothing--EPEN would be nothing," said Stavros Viglis, a merchant who said he and his wife had come from West Germany, where they live, at their own expense, especially for the rally.

Some in the crowd, made up of prosperous-looking Athenians in dark three-piece suits accompanied by wives in fur coats mixed with more casually dressed supporters from the provinces, wept openly as Papadopoulos' voice sounded over loudspeakers, delivering an address taped in prison and spirited to the meeting.

Using rhetoric reminiscent of the seven-year dictatorship, Papadopoulos pledged to pull Greece out of the "gravest political stalemate of its postwar history," to restore the values of "Hellenic Christian civilization" and to bring back law and order to Greek youth in schools and universities.

European Community analysts ruled out the possibility of any European pressure for Papadopoulos' release even if he were to win a parliamentary seat.

But political observers in Athens said the creation of the new party could have repercussions for New Democracy, which in the 1981 national elections served as an umbrella for voters ranging from the center to the far right.

Analysts said the decision to run with the extreme right, which is estimated at about 6 percent of the Greek electorate, cost New Democracy much greater numbers of centrist votes and was a significant factor in the conservatives' crushing election defeat at the hands of the Socialists.

"EPEN could pull the far right-wing vote from New Democracy. But that might be doing the party a favor, by allowing centrists to come back," one observer said.

Officials said the new party currently has 15,000 members nationwide and 3,000 among Greeks living abroad, with 105 local offices scattered throughout Greece. They said the party is functioning on private contributions from supporters.