The Basque Nationalist Party (PNV), the major political force in the tension-ridden Basque province, decided today to boycott Spain's parliament. The action has plunged the government policy on the explosive regional issue into disarray and worsened already strained relationships between the central administration and the restive northern provinces.

The Basque Party alleged that the government was stonewalling the transfer of administrative and political power to the Basque region, which gained self-government last year along with the rich northeastern region of Catalonia. Its executive committee ordered the eight party congressmen and seven senators to temporarily withdraw from parliament until the government demonstrated that it was firmly committed to decentralization.

The Basque stand comes shortly after the government announced a major policy shift on the regional question, saying that it would slow down the pace of the devolution of power to the regions. In taking the action, the Madrid authorities cited the allegedly insurmountable costs of the task of dismantling the tight centralism it had inherited from the Franco regime.

The policy shift, announced Wednesday, provoked an immediate outcry from the left and from regional parties that are seeking the self-government gained by the Basques and Catalans. The protest was strongest in the depressed southern region of Andalusia where large landed estates and agrarian unemployment go hand in hand. Andalusia was next on the list for self-government until the policy shift and opposition groups there have called for a general strike on the issue for Jan. 25.

The government's decision to slow down decentralization provoked the resignation this week of the minister of culture, Manuel Calavero Arevalo, and the first cabinet reshuffle since the general elections last March 10. Arevalo was deeply committed to Andalusian autonomy.

Sources close to the government said that the Basque boycott was a dangerous move which reflected a widening rift between the Basques and the Madrid administration. The real fear, the sources said, is that in elections scheduled March 9 for a regional Basque parliament the issue will be Basques against Spaniards, thus firing the deeply-rooted secessionist sentiments among large segments of the Basque population.