Belgrade — ''It is a constant tug of war,'' says silver-haired Najdam Pasic, noted Serb historian and current president of Yugoslavia's Constitutional Court. Professor Pasic is the watchdog of a Constitution under which Yugoslavia's republics and regions - a ''Joseph's coat'' of many ethnic peoples - are equals according to the Constitution.
He does not disguise his view that the country is facing its worst economic crisis ever and that it needs a stronger hand at the federal helm. Or that equality has encouraged local rivalries that are partly responsible for Yugoslavia's current difficulties.
Five years ago, under the same Constitution, there was an authoritative and firm federal hand - that of President Josip Broz Tito.
That authority was sorely missed in the autonomous province of Kosovo in 1981 . There, just a year after Tito's passing, Albanians held protests demanding that Kosovo be made a republic. The province has since been ''pacified,'' but its indigenous problems remain.
For Yugoslavia as a whole, Pasic says, there can be only one course through the present crisis: open, critical dialogue and acceptance of pluralism of interests, both within and outside the party. (Pasic is a member of the Central Committee of Yugoslavia's Communist Party.)
Pasic's view, of course, includes pluralism for the republics, but their equality, he says, has been exploited too far for the national good. The federal interest in essential areas is too often weakened by a system in which eight hands tug at the tiller - in the name of six republics and the two autonomous provinces.
Each unit, with its own set of local problems and interests, tends increasingly to have a view of itself as more equal than the others. That Orwellian phrase is a simplification. But to a very considerable extent it does fit the contemporary scene in which Yugoslav interest is too often thwarted by localism and by conflicts over the level of funds set aside for development.
The conflicts over money for development have been there from the start. And the disparities remain, despite a massive development fund levied from the advanced republics of the north to help the backward brothers of the south - above all, Kosovo.
''Brotherhood and unity'' - the title of Tito's first constitution - remains unaffected, in theory, by subsequent constitutional revisions and amendments. But each bit of rewriting increased local freedoms.
This did not matter so much in the economic ''boom'' of the 1970s. But after five years of steady downturn, it is obviously something the country can no longer afford on the old prodigal scale.
The Constitution, as Professor Pasic say, recognized ''states' rights'' but implied due regard for federal interest in key national areas, such as communications and energy. Even here, though, consensus is required.
Increasingly, however, federal authority has scarcely seemed to exist. Ideas, papers, and resolutions have too often gone chattering to and fro over the telex lines between Belgrade and the provinces in an often-unproductive search for agreement that any of the local governments can frustrate, should it choose to do so.
This year saw a battle royal between the central government and the republics over the International Monetary Fund's conditions for a one-year, $375 million standby credit. The government reached the agreement only after an uncompromising warning from federal Prime Minister Milka Planinc.
It was a painful package and potentially, a politically sensitive one. But it was unquestionably essential to Yugoslav economic survival and revival.
''The republics,'' Pasic says, ''have stood out for consensus on everything, way beyond the broad issues. In effect, they have a right (of) veto on matters of all Yugoslav interest and necessity and do not hesitate to use it.'' For example, he says, a Yugoslav federal railroad exists - but in name only.
''International trains crossing Yugoslavia are involved in five transit tariffs - one is European and the others are operated by four of our republics. There is no uniformity even of equipment. Some republics buy French locomotives, some buy Swiss or other makes. Does it make sense?''
Yugoslavia, in fact, seems often to have eight of everything besides its eight territorial units and their local administrations. There are eight communist parties (beside the federal one), which can also mean eight variations in liberal or hard-line interpretations of the basic Communist Party statute of ''democratic centralism.''
There is no universal price structure. Prices and exchange rates vary wildly in trade between the republics.
And there is frequent conflict between the National Bank and provincial banks which flout the former's reinforced authority to curb local investment excesses through new ''tight money'' criteria vital in the battle against the current economic crisis.