Spain has passed the point of no return in the post-Franco reconstruction of a federalist state, constituting a complete break with the authoritarian centralism that characterized the government of Generalissimo Francisco Franco.

An agreement reached today between the Madrid administration and politicians representing the northeastern area of Catalonia was the second home-rule pact in less than a month. A similar agreement on July 18 ensured self-government in the near future for the Basque provinces in the north.

The granting of greater powers to the provinces was a mojor demand of opponents of Francoism. The democratic constitution approved by referendum in December last year ensured the creation of "autonomous communities" to replace the all-powerful Madrid bureaucracy. The agreements with Catalonia and the Basque provinces pave the way for the reorganizing of all provinces into self-governing areas with a federal structure as the end result.

The willingness of the ruling Union of the Democratic Center party and of Premier Adolfo Suarez's government to negotiate home-rule bills rapidly following the proclamation of the constitution is a response to the powerful nationalist feelings that became vocal once democracy was restored to Spain. Home rule was a major issue in the programs of all parties contesting parliamentary seats in Catalonia and in the Basque provinces.

Both Catalonia and the Basque provinces will hold referendums wihtin the next three months that are expected to return a massive endorsement for the agreements. Both areas could be self-governing next year, after holding elections to form a local parliamentary assembly.

In the case of the Basque provinces, the devolution of local power was considered politically necessary to isolate the terrorist independence movement of the ETA. In Catalonia, there is no similar guerrilla organization but in the past two years the celebration of Catalonia's "National Day" on September 11 has brought hundreds of thousands into the streets in peaceful demonstrations.

"Autonomous communities" was the term employed in the constitution to avoid the explicit use of "federalism a concept that was at the root of civil wars and short-lived governments since the last century. The semantic alteration also served to pacify conservatives who hold firmly to the centralism imposed by Franco with the motto, "Spain: one, great and free."

Nevertheless, the new home-rule agreements go beyond the self-government enjoyed by Cataloniia and the Basque region during the Spanish Republic until they were conquered by the Nationalist forces in the civil war.

Andreu Abello, a veteran Catalan nationalist who presided over the Supreme Court of Catalonia during the republic, was optimistic about the agreement for his community. Abello, currnetly a Socialist senator for Barcelona, said: "The present home-rule bill is an improvement on the one legislated during the republic and which was crushed by Franco. This is undoubtedly a positive achievement for all concerned."

Among the innovation of the new home-rule bills are provisions making Catalan and Basque the offical languages in those areas. Under Francoism, Catalan and Basue cultural movements were treated as separatist tendencies and ran afoul of the police. The use of Catalan and Basque was frowned upon.

The bills also encompass wide-ranging measures covering control of taxation, the judiciary, local ploice forces and public works. As such they form the framework for future pacts between the central administration and other provincial groupings such as Galicia in the northwest, Valencia in the east and the Canary Islands.

While it is generally agreed that the home-rule bills have successfully acted out the letter of the constitution and difused tensions, few doubt the practice of self-government will in itself generate new problems.

If the movement towards self-government was unstoppable, particularly in those areas that had enjoyed it in the past, the agravation of existing regional inequalities is just as much a potential powder keg.

The essential problem is the cost involved in maintaining a federalist state structure.

"Federalism is fine for the U.S. or West Germany, but nobody here has stoped to think whether we can afford it," one administration official said.

In its desire to prevent the creation of "privileged areas" -- Catalonia and the Basque provinces together provide more than half of the Spanish tax income -- the government has insisted that the richer "autonomous communities" share the burden of the more depressed regions with the administration in Madrid. CAPTION: Map, no caption, By Dave Cook-The Washington Post