More Cash Is Offered for Oil Partnerships : Investment: The 137,000 limited partners in the Prudential Securities group would still lose about $340 million.

A Texas oil company boosted its cash offer Monday for a troubled group of Prudential Securities oil and gas limited partnerships by $42.5 million to $508 million--a purchase price that still would leave investors with about $340 million in out-of-pocket losses.

Parker & Parsley Petroleum said $491 million of the total would go to limited partners--the 137,000 thousand investors, many of them retirees, to whom Prudential sold partnership interests from 1983 to 1990.

The firm also extended to June 21 the deadline for investors to tender their interests in the partnerships, known as the Energy Income Funds.

Prudential said Parker & Parsley was able to increase its offer because it agreed to sell part of the funds’ oil and gas properties to Louis Dreyfus Natural Gas Holdings Corp. for about $157 million.

The enhanced offer follows efforts to settle a dispute about the way Prudential handled bidding between the two firms: It accepted the Parker & Parsley over a higher offer by Dreyfus and did not disclose that the higher offer had been made.

The offer now equals Dreyfus’ bid.

Parker and Parsley said the new offer also includes an additional $2.5 million in cash for individual investors, correcting what it described as a “clerical error” that miscalculated how the money would be shared with the funds’ general partners.

Individuals invested $1.44 billion in the partnerships and received back $650 million in cash distributions. If they accept the new offer, they will have received back $1.1 billion--leaving about $340 million in out-of-pocket losses.

The partnership sales have resulted in numerous lawsuits against Prudential by investors and pending investigations by the Securities and Exchange Commission and state criminal authorities and securities regulators. Prudential has denied any wrongdoing.