* Merkel cabinet minister gave SPD advance warning of probe
* SPD lawmaker Edathy has denied child porn allegations
* Departure could aggravate tensions in coalition (Adds comments from Gabriel)
BERLIN, Feb 14 (Reuters) - A senior German minister resigned on Friday amid accusations he leaked confidential information about a fellow lawmaker suspected of possessing child pornography, dealing a blow to Chancellor Angela Merkel and her two-month old government.
The resignation of Agriculture Minister Hans-Peter Friedrich, the latest in a series of cabinet departures under Merkel, could aggravate tensions in Berlin's new "grand coalition" at a time when it is trying to push through complex reforms of pensions and renewable energy.
"The pressure on me has grown so much in the last couple of hours that I no longer think I can do the job in the agriculture ministry with the required concentration, calm and political support," Friedrich told a hastily-called news conference.
Merkel said she had accepted Friedrich's resignation "with great respect and great regret", adding that it was too early to discuss who would succeed him.
The resignation follows questions about whether Friedrich, a member of Merkel's Bavarian sister party, inappropriately passed on confidential information about a looming investigation into a prominent Social Democrat (SPD) lawmaker to the leader of the SPD.
Friedrich was interior minister in the previous centre-right government at the time.
It emerged this week that the SPD lawmaker, Sebastian Edathy, is being investigated by prosecutors, who suspect him of possessing child pornography, an accusation Edathy has vigorously denied.
The 44-year-old Edathy, well known in Germany for leading a 2012-13 inquiry into neo-Nazi killings, resigned from parliament last week, citing health reasons, and has threatened to sue the newspaper that first reported about the child porn suspicions earlier this week.
WHO TIPPED OFF EDATHY?
What started as a small domestic affair erupted into a major political scandal on Thursday when it emerged that Friedrich had informed SPD chairman Sigmar Gabriel in October that Edathy could become the target of an investigation.
Gabriel then passed that on to two other senior members of his party -- Frank-Walter Steinmeier, now foreign minister, and Thomas Oppermann, who leads the SPD in parliament.
Prosecutors in Hanover, who are investigating Edathy, have complained that the leaking may have compromised their case.
Edathy appears to have been given advance warning of the investigation, Hanover prosecutor Joerg Froehlich told a news conference on Friday.
As a result, German media have reported, relevant information on Edathy's computers may have been destroyed.
It is still unclear who tipped off Edathy. If it emerged that he was alerted by a senior SPD member, it could cause even greater upheaval in Merkel's coalition.
"This was turbo crisis management by Merkel," said Tom Jaeger, a political scientist at the University of Cologne.
"She's trying to keep the issue out of the public because no one knows what might come out of this. There are top people in the coalition like Gabriel and Oppermann involved."
The big outstanding question is how Edathy was tipped off.
Speaking on German public broadcaster ARD, Gabriel - now Germany's Economy Minister - said neither he nor Steinmeier nor Oppermann had informed Edathy. Gabriel told mass-selling newspaper Bild he therefore ruled out personnel consequences in the SPD.
Gabriel defended Friedrich on ARD, saying the former interior minister had used his discretion at a time when personnel decisions were pending in the SPD.
"He tried to avert damage and looking at it now, he succeeded in doing that," Gabriel said.
Friedrich has said he believes he acted in accordance with the law by informing the SPD, which was in coalition talks with Merkel's conservatives at the time and may have been considering giving Edathy a senior post in the new government.
Friedrich's resignation is the latest in a string of departures of top conservative ministers under Merkel since she took power in 2005.
Education Minister Annette Schavan, a close friend and ally of the chancellor, was forced out last year over allegations of plagiarism, two years after Defence Minister Karl-Theodor zu Guttenberg left for the same reasons.
Environment Minister Norbert Roettgen was fired in 2012 for bungling an important regional election for the conservatives. Franz Josef Jung, a former defence and labour minister, left in 2009 over his handling of a deadly air strike in Afghanistan. (Additional reporting by Thorsten Severin, Gernot Heller, Stephen Brown, Noah Barkin and Michelle Martin; Editing by Noah Barkin and Ralph Boulton)