* NordLB looking for about 3 billion in fresh capital -sources
* Rival bids from Helaba, Apollo, Cerberus and Advent -sources
* Final bids due end-Nov -sources (Adds bidder names, background)
By Arno Schuetze and Hans Seidenstuecker
FRANKFURT, Oct 24 (Reuters) - Commerzbank has made a non-binding offer to take a stake in German NordLB, people close to the matter said, as an auction for the ailing public-sector lender progresses.
NordLB aims to boost its capital by about 3 billion euros ($3.4 billion) to cope with bad ship loans and has asked for final bids by the end of November.
The bank is working on a restructuring plan that includes bringing in a new investor.
Public-sector peer Helaba as well as private equity investors Apollo, Cerberus and Advent also handed in tentative bids earlier this month.
NordLB, Commerzbank and the other bidders declined to comment or were not immediately available for comment.
The bank and its shareholders - the German state of Lower Saxony and regional savings banks - want to restructure the bank in a way that avoids breaching European Union state aid rules as this could force an unwanted complete sale.
To do so, NordLB is seeking a capital injection from Lower Saxony and wants to sell a stake to a third party to show that any investment occurs at market prices.
NordLB is active in financing companies, real estate, infrastructure and the transport sector. It has been dragged down by its exposure to the shipping industry, which has been going through its worst slump on record, leaving NordLB with 7.7 billion euros in bad loans as of June 2018.
NordLB is already in the market with a 2 billion euro slice of those loans, which it expects to sell at a hefty discount to face value, the sources said, adding that further portfolio sell-downs were expected once that deal is completed.
Handelsblatt earlier reported that Commerzbank has made a bid for NordLB. ($1 = 0.8769 euros) (Reporting by Hans Seidenstücker and Arno Schuetze Editing by Alexandra Hudson)