BERLIN, Sept 13 (Reuters) - Germany earned more than 4 billion euros ($4.72 billion) by issuing new bonds in the first eight months of this year as negative yields continue to push down Berlin's overall debt servicing costs to unprecedented lows, a government document showed on Monday.

The lower-than-expected borrowing costs are enabled by the European Central Bank's loose monetary policy and Germany's international reputation as a fiscally reliable country, resulting in negative interest rates even for longer maturities.

In a letter seen by Reuters following a parliamentary request, Deputy Finance Minister Sarah Ryglewski told opposition lawmaker Fabio De Masi that the government issued bonds worth more than 275 billion euros in the first eight months of 2021 to finance the federal budget and special funds.

A total premium of 4.25 billion euros was received in these auctions, Ryglewski wrote, adding that the average issuing yield was -0.55% and the average bid-to-cover ratio stood at 1.72.

"The federal government could have sold even more bonds in the auctions. On average, there were significantly more bids from the banks than bonds sold," De Masi of the far-left Linke party told Reuters in an email.

The figures showed that Germany could grow out of its debt in the coming years without any problems and that there was no need to return to strict borrowing limits from 2023 onwards as suggested by Finance Minister Olaf Scholz, De Masi wrote.

"If we return to the debt brake too quickly, there is a risk of choking off the economic recovery, public investment and the welfare state," De Masi added.

Returning to the fiscal rules of the debt brake would be "economic madness" given the investments needs to reach climate protection goals, he added. "The federal government even earns money with debt - and we are facing the greatest restructuring in industrial history through climate change and digitisation."

Scholz is financing the government's COVID-19 emergency measures with record new borrowing of up to 240 billion euros this year and more than 130 billion euros last year for which parliament suspended the debt limits in the constitution.

Scholz, the centre-left Social Democrat candidate to succeed conservative Angela Merkel as chancellor in a Sept. 26 election, has proposed suspending the debt brake for a third year in a row in 2022 to allow additional borrowing of nearly 100 billion euros next year.

From 2023 onwards, Scholz wants to consolidate public finances and return to the debt brake rule which would limit new borrowing to 0.35% of economic output. So this would allow only reduced deficit spending of 10-15 billion euros each year. ($1 = 0.8483 euros) (Reporting by Rene Wagner and Michael Nienaber; Editing by Andrew Heavens)