WASHINGTON (AP) _ MCI WorldCom has fully implemented an electronic trading network for Nasdaq Stock Market that will enable it to handle up to 4 billion shares traded per day, the companies announced Wednesday.

The new system, which will be maintained by MCI, more than doubles the speed and capacity of Nasdaq's previous electronic trading network.

The upgraded network can handle up to 4 billion shares traded per day, and can be scaled up to accommodate an 8 billion share day, they said. Nasdaq has averaged 985 million shares traded per day in 1999, with a peak of 1.4 billion shares traded on April 14.

The companies said the new network enables subscribers to receive a message simultaneously after a broker enters it and guarantees delivery of time-sensitive data.

MCI signed a $600 million contract in November of 1997, to replace Nasdaq's existing electronic trading network, also designed by MCI.