NEW YORK (CNN/Money) - Shares of Electronic Data Systems Corp. tumbled Monday after the company warned revenue and earnings in the second half of the year could take a hit from trouble at WorldCom Group, on the same day it announced the unsuccessful end of contract talks with Procter & Gamble Co.

Plano, Texas-based EDS said that, "in certain downside scenarios," trouble at WorldCom, one of its customers, could impact its operations in the last two quarters of 2002. EDS' contract to provide WorldCom with information technology (IT) services contributes between $160 million and $175 million to quarterly revenue and between 3 cents and 4 cents per share in quarterly earnings, EDS said.

WorldCom shares were nearly worthless Monday after the company's announcement that it might have more accounting messes to uncover. It revealed last week that it would have to cut some $3.8 billion in revenue from past financial statements after finding improper accounting. The Securities and Exchange Commission has charged WorldCom with fraud related to those statements.

EDS (EDS: down $5.62 to $31.53, Research, Estimates) said it has an 11-year, $6.4 billion contract with WorldCom that was signed in October 1999. Also in 1999, EDS signed an 11-year, $6 billion contract to get telecommunications service from WorldCom.

EDS said WorldCom would owe it $150 million by the end of the second quarter and that WorldCom's payments were "substantially" current. WorldCom said Monday that it had defaulted on some of its loans, and there is widespread speculation that the company could end up in bankruptcy.

In more bad news, EDS said it had ended negotiations for a potential outsourcing contract with Procter & Gamble that was valued by some analysts at about $1 billion.

P&G (PG: up $1.05 to $90.35, Research, Estimates), which makes Crest toothpaste, Tide laundry detergent and a host of other consumer products, is looking for an outside firm to handle its IT systems. Reuters, citing industry sources, reported in June that the contract could have been worth $1 billion.

Another finalist for the P&G contract was Affiliated Computer Services Inc. (ACS: down $0.48 to $47.00, Research, Estimates), Reuters reported in June.