UPDATE 1-German Kruemmel reactor grounded for months

* Operator Vattenfall Europe says to replace transformers

* Plant director leaves

* Co-owner and operator E.ON says to stay involved

(adds details from Vattenfall, local ministry, E.ON)

FRANKFURT, July 7 (Reuters) - Swedish-German utility Vattenfall AB [VATN.UL] said on Tuesday its Kruemmel nuclear power plant in northern Germany will stay offline "at least" for several months, as it must replace its two transformers.

Vattenfall reacted to two botched recent restarts of a plant which had been down for two years due to safety issues, shutting the controversial reactor during a heated political debate over nuclear energy ahead of national elections in September.

The move also confirmed that some 1,400 megawatts of output capacity will be missing in the national electricity balance, but this is less than one percent of overall supply.

Vattenfall peer E.ON (EONGn.DE), which owns a 50 percent stake in Kruemmel, meanwhile said it had no reason to pull out of the troubled power station.

E.ON CEO Wulf Bernotat said at a conference in Paris the shutdown was purely linked to the transformer issues.

Vattenfall said first results of investigations into events last weekend, when the plant switched itself off, showed a transformer monitoring device had not been installed.

"By deciding to swap the transformers, we have opted for a decisive course of the highest possible security," said the head of Vattenfall's German arm, Tuomo Hatakka, in a statement.

He also said that the plant's current director, Hans-Dieter Lucht, had left his position, and that Vattenfall had asked Walther Stubbe to take on his job temporarily.

A further report will be due on Thursday, he said.

The ministry responsible for nuclear supervision in Schleswig-Holstein state, where Kruemmel is situated, welcomed Vattenfall's moves to exchange the transformers but added the discussion about the plant's future had not been resolved.

It also said that Vattenfall during the recomissioning at the end of June had not fully followed required steps, which had left it unaware of certain flaws, which later escalated.

The incidents have sharpened the battle lines within the Berlin coalition government on how quickly and at what intervals German nuclear capacity of 21,497 MW overall should be shut.

Conservatives still want to relax the time schedules while nuclear opponents call for a quicker withdrawal.

(Reporting by Vera Eckert)