The decision of the Green party in Hesse to ''tolerate'' Social Democratic Premier Holger Borner in the state legislature's June 6 vote on the budget has broad implications for West German politics.
* Within the countercultural Greens it adds to the weight of the ''realos'' (for ''realpolitiker,'' or pragmatists) as against the ''fundamentalists.'' The latter want to remain a pure protest ''antiparty party'' that will never compromise as other politicians do.
* For the Social Democrats, the Hesse semi-coalition keeps alive the possibility - however remote - of an eventual coalition of the left at the federal level.
The Greens pride themselves on their decentralization, and the recent decision of party members in one state hardly obligates Greens elsewhere to follow their example.
Nonetheless, the evolution of the Hesse Greens into a real dealmaking party - they had been one of the most radical of any of the party's regional groups - lends respect to such pragmatism.
This is no coalition, the Greens stress. Their 15 votes will finally give Mr. Borner - whose Social Democrats hold only a plurality in the Landtag - the majority he needs to pass his budget.
But the Greens will not join his government. They insist their cooperation is conditional and subject to reconsideration. In particular, they want Borner to outlaw disposal of poisonous chemical waste in the Mainhausen dump. He says he cannot accede to this since he doesn't want to ''drive the chemical industry out of Hesse.''
Even so, the 70 percent approval of toleration by the thousand party members participating in the May 19 Green convention is something of a landmark. It ends six months of inter-party negotiations and intramural Green factional fighting.
It will allow Borner (who has been acting head of the state government for a year and a half) to become official premier - if the cooperation doesn't founder on the Mainhausen dump.
The victory of the Green pragmatists is a personal triumph for ex-pastor and state Green legislator Karl Kerschgens and Bundestag member Joschka Fischer. Kerschgens set the tone of the convention in arguing that he thought it was better to settle for gradual reforms than to achieve less by aiming for impossible revolutionary transformation.
The cooperation of the two parties is likely to be stormy. Borner has not accommodated the Greens on several causes close to their heart: halting construction of the new Biblis nuclear power plant, taking an antinuclear missile stance, banning night flights at the Frankfurt airport, or stopping prison construction.
The ''realos'' acknowledge these failures but consider them less important than the victories. Social Democratic concessions to the Greens include the guarantee that children up to the age of 18 may come to Hesse to join parents who are foreign ''guest workers'' there.