In what may be the largest settlement of its kind in history, the government announced yesterday that it has agreed to pay the Penn Central Railroad a total of $2.1 billion, including interest, for properties the railroad turned over to Conrail in 1976.

The agreement, which still must be approved by a special three-judge federal court, places a $1.46 billion value on the Penn Central properties in 1976 dollars. Interest since 1976 at the statutory rate of 8 percent, compounded annually, amounts to $653 million, bringing the total price to be paid Penn Central to $2.113 billion.

Thomas G. Allison, general counsel of the Department of Transportation called the settlement "advantageous" for the government. In litigation since 1976, Penn Central had claimed the properties were worth up to $6 billion while the government had contended they were worth between $500 million and $600 million.

Allison said a significant part of the settlement called for Penn Central to relinquish its right to Conrail stock, which will be returned to the United States Railway Association, a government corporation which acts as Conrail's banker and also monitors its operations. "Government retention of the stock, rather than permitting its ownership to be diffused for private speculative purposes, will facilitate the planning process and any physical or corporate restructuring of Conrail that may be required," Allison said.

"It is the continuing policy of the United States to achieve a private-sector solution to the problems caused by the bankruptcies of the eastern railroads," Allison said.

Penn Central was the largest of seven major bankrupt railroads in the Northeast and Midwest that transferred properties to Conrail -- the Consolidated Rail Corp. -- the federally subsdized private-sector operating entity created by the Regional Rail Reorganization Act of 1973. The act also created a special court empowered to order the conveyance of bankrupt rail properties to Conrail and others in order to preserve rail service in the region and also to resolve the issue of the amount of compensation to be awarded to Penn Central and the others for the property conveyed to Conrail.

The settlement agreement announced yesterday represents about 80 percent of the total claims arising out of the creation of Conrail. "We hope that today's agreement is a precursor to settlement of these other claims as well," USRA Chairman Stephen Berger said yesterday.

Altogether, assets conveyed to Conrail under the 3R Act included 19,000 miles of rail lines, 400,000 acres of land, 185,000 pieces of rolling stock, 5,000 locomotives and 4,000 buildings. The agreement announced yesterday covers about 14,000 miles of rail lines, 220,000 acres of property in 15 states, including the District of Columbia, 4,000 locomotives and 134,000 freight cars.

In announcing the agreed-to-settlement with the government, Penn Central Corp. said yesterday it is conducting conversations with Gk Technologies, a telecommunications company, concerning possible modifications of the proposed arrangement for the acquisition of GK by Penn Central, which was previously announced. A government lawyer said yesterday the settlement allows Penn Central to buy the company. Penn Central has not been in the railroad business since 1976. Its principal activities are now in energy, marine and industrial equipment, and living and leisure services.