Bernard L. Madoff’s massive investment fraud, which eluded federal regulators until it collapsed in 2008, began as early as the 1970s, according to a new guilty plea by a longtime Madoff employee.

David L. Kugel, 66, admitted to helping Madoff create fake, backdated trading records beginning in the early 1970s, the Justice Department said.

Kugel pleaded guilty Monday to six criminal counts, including conspiracy, securities fraud and bank fraud. He faces sentencing in May.

The long-running fraud took in $170 billion, the government said in its case against Kugel. Investors lost an estimated $20 billion.

Kugel went to work for Madoff in 1970 and was with the firm until about the time of Madoff’s arrest. He was a securities trader and a compliance analyst, the government said.

But Madoff was actually running a giant Ponzi scheme in which he created the illusion of trading profits and used money from some investors to make payouts to others.

Kugel regularly furnished historical information that other Madoff employees used to fabricate trades, the government charged. That included the names of stocks and the price ranges in which they had traded on particular dates, the government said. To make sure the fictitious trades would not exceed what was possible, he also provided the total volume of shares of individual stocks traded on those days, the government said.

Kugel told colleagues how much profit he wanted his accounts with Madoff to earn, and he supplied information for trades he wanted reflected in his accounts “long after their purported settlement dates,” the government said.

To secure millions of dollars of bank loans — for example, for homes in Boca Raton, Fla., and Long Island — he and others prepared false documentation of the amount he had on deposit with Madoff, the government said.

From 2001 to 2008, Kugel withdrew almost $10 million from his Madoff accounts, according to the Securities and Exchange Commission, which filed civil charges against him. In the final years of the fraud, his annual pay was as much as $588,000, the SEC said.

Kugel’s agreement with the government calls for him to forfeit $170 billion — including such itemized possessions as Rolex, Cartier and Patek Philippe watches; a Mercedes and a treadmill.

Under the deal, the U.S. attorney’s office in Manhattan agreed not to contest the claim of Kugel’s wife, Phyllis Kugel, to almost $1.2 million — which amounts to about $791,000 after authorized expenses. She is permitted to keep some personal effects, including her engagement ring, wedding band and her mother’s pearls.

Madoff pleaded guilty to fraud in March 2009 and is serving a 150-year prison sentence.