The battle lines are clear. On one side stands Venceslas Kruta, clean-shaven and dressed in an impeccable suit and tie. After spending much of his youth in Czechoslovakia, he is a fervent anticommunist.

On the other stands Pierre-Jean Trombetta, bearded, bespectacled, and dressed in jeans, with a raggedy shirt flying out of his pants in all directions. He is a member of the Communist Party.

Naturally, the two men detest each other. Each accuses the other of bad methodology and bad results - all of which is also natural, except they are not fighting about politics or economics.

Their brawl is over archaeology.

Mr. Kruta and Mr. Trombetta are both completing prestigious excavations of the courtyards of the famous Louvre. The dispute between the two has become a cause celebre here, illustrating how ideology in this most ideological of countries disrupts even the most innocent sounding of projects.

''It sure shows something about France in 1984 when archaeology becomes divided by ideology into right and left,'' Kruta says. ''It's become folklore.''

The folklore began last year when President Francois Mitterrand approved a controversial proposal to modernize and enlarge the Louvre. Along with the hotly debated decision to install a glass pyramid designed by architect I. M. Pei for an entrance, the President allocated money for archaeological exploration of the venerable palace's two courtyards.

One was to uncover the remains of the 12th-century medieval dungeon of Philippe Auguste. This is Kruta's dig.

''The dungeon symbolizes the state,'' he explains. ''It's where the king guarded everything valuable to him, his treasury, his crown - and just as important, his most important prisoners.''

The other was to uncover the working-class neighborhood outside the medieval walls. This, of course, is Trombetta's dig.

''We're trying to reconstruct the life of the people,'' he says. ''We want to find out who lived here, how they lived, and how their lives changed between the 14th and 16th centuries.''

Enter the Kruta workplace, and bulldozers plow away. Objects found are transported by conveyor belt to modern laboratories. Workers all wear hard hats: They are professionals paid industrial wages. Is this a construction site or an archaeological dig?

''We have one year to complete this project,'' Kruta answers. ''To finish in time, we have to approach the project as an enterprise, efficiently, not like Boy Scouts. If we used spoons all the time, then all archaeology in France would soon have to stop.''

The jibes hit. Enter the Trombetta worksite, and the only sound is of hand tools scraping the ground. Jeans are everywhere, there is not a hard hat in sight. The volunteers mix easily with the professionals, making jokes, fooling around. Is this a commune?

''We have a body of professionals, but the volunteers should have a chance to work here and learn,'' responds Trombetta. ''Archaeology students have no other chance to learn.''

None of these differences would have amounted to more than a passing curiosity if Trombetta hadn't told a reporter that ''there is an archaeology of the right and one of the left.'' He went on to decry Kruta's ''rightist'' methods as unprofessional and threatening to plow under valuable objects.

Kruta was incensed. He calls Trombetta's charges ''ridiculous,'' saying that careful soundings were taken before digging and that for a one-meter area around the dungeon walls, all digging is done by hand.

''There is no loss of important information,'' he affirms, pointing to a piece of jewelry no bigger than five centimeters.

''We even recover objects this small. If I was a Marxist, Trombetta would probably say my methods were revolutionary.''

Beneath the verbal war, work on both digs is proceeding pretty much normally.

Kruta's dungeon walls are emerging, their medieval turrets menacing and impressive. The work is scheduled to be completed Jan. 1, then opened to the public as a permanent exhibition.

''Napoleon III wanted to dig for the dungeon, but he didn't have the money to do it,'' Kruta says. ''An important part of our history now will be recovered.''

Outside the old dungeon walls, Trombetta and his volunteers have brought up some 5,800 pieces of glass or ceramic ware. They have also uncovered hundreds of old coins, utensils, jewelry, and other artifacts.

Digging will continue until 1986. Meanwhile, Trombetta plans to hold his university-level urban archaeology courses at the site. After the work is completed, he will write a ''new history'' of the neighborhood while the dig itself is covered up for the construction of Mr. Pei's pyramid.

A final question hangs over both operations: Are they worth it? Their combined budget amounts to some 50 million francs (more than $5 million), equal to the entire budget for all the rest of the archaeological digs in France.

Many distinguished archaeologists have been angered more by the choice of both sites than by the ideological quarrel. They say that not much of worth will be found in either excavation.

Once again, Kruta and Trombetta disagree.

''It's a false criticism,'' says Kruta. ''The money is here for this operation, and it can't be used elsewhere. That's what President Mitterrand says.''

''It's true,'' retorts Trombetta. ''The site isn't just that important. It's Mitterrand's big prestige project.''

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