* Education minister stripped of PhD awarded in 1980
* Schavan to take legal action, resists calls to resign
* Merkel allies see campaign to damage gov't before vote
BERLIN, Feb 6 (Reuters) - Angela Merkel's education minister said on Wednesday she would take legal action against a decision to void her doctorate for alleged plagiarism, an untimely distraction for the German chancellor ahead of September's national election.
German opposition lawmakers said Annette Schavan, a close Merkel ally, should resign after the University of Duesseldorf said on Tuesday that parts of her 1980 doctoral thesis had been copied and that it was stripping her of her PhD.
Her case closely mirrors that of Karl-Theodor zu Guttenberg, who quit as Germany's defence minister in 2011 over a plagiarised thesis. Guttenberg had been viewed before his departure as a possible heir to Merkel.
"I will not accept the decision of the University of Duesseldorf and I will file a lawsuit against it," Schavan, 57, told reporters during a visit to Johannesburg, South Africa.
She declined to make any further comment for legal reasons.
The accusations of plagiarism are especially embarrassing for Schavan because she oversees Germany's universities and had previously been scathing in her criticism of Guttenberg, who resigned a month after losing his doctorate.
"An education minister who is proven to have grossly violated academic rules cannot continue in the post," said Renate Kuenast, a leading member of the opposition Greens.
"I assume that Frau Schavan will spare herself and education a prolongation of this affair by resigning."
Merkel has not publicly commented on the Schavan case. But members of her centre-right coalition said the minister had fallen victim to a politically motivated campaign to damage the government ahead of the autumn federal election.
But German media were mostly critical of Schavan.
"If the education minister has cheated in her doctoral thesis, it is like the finance minister secretly hiding away his money in Switzerland or the traffic minister driving a car while drunk," said the top-selling Bild newspaper.
"There is no alternative (to resignation) for her."
In Tuesday's ruling, the Duesseldorf University commission said Schavan had "systematically and intentionally presented intellectual performance that in reality she did not generate herself".
The decision left Schavan without an academic title, an important symbol of status in German politics and business, as her degree programme in philosophy finished solely with a PhD.
Since the allegations first arose in May last year, Schavan has repeatedly denied wrongdoing and said she wrote her dissertation with a clear conscience.
Her lawyers have said the proceedings of the commission had been riddled with mistakes and were unlawful, not least because information was leaked to the public in the process.
Merkel, who holds a doctorate in physics, is Germany's most popular politician and her conservatives are tipped to win September's election.
But Merkel's current coalition partner, the liberal Free Democrats, may fail to clear the 5 percent threshold to enter parliament, which would force her to consider an unwieldy pact with the opposition Social Democrats. (Reporting by Shafiek Tassiem in Johannesburg, Gareth Jones and Madeline Chambers in Berlin; writing by Gareth Jones; editing by Mark Heinrich)