For the second time during his rocky struggle to live with an artificial heart, William J. Schroeder was discharged today from Humana Hospital Audubon. He showed signs of a surprising recovery from a debilitating stroke.

Schroeder, 53, had moved in April across the street to the apartment where he went today but was readmitted a month later when a severe stroke left him weak, groggy and for weeks unable to talk.

Saturday night, however, according to his son Stan, 28, "We couldn't get him to be quiet at all . . . that's all he could talk about: 'Let's go, let's go, let's go.' "

Schroeder was buoyed by a visit last Sunday to his home in Jasper, Ind., the first time he had made the 90-mile trip since his implant nearly nine months ago. "I don't think he wanted to come back . . . . that's what he was working for all the time," Stan Schroeder said.

Today, Schroeder appeared more alert and responsive than during his Jasper visit or his previous discharge, when relatives had to direct his attention to crowds and help him wave.

Dr. William C. DeVries said last week that he is not sure what accounts for what he termed Schroeder's "amazing" recovery from the stroke, the second one since DeVries replaced his diseased heart with a plastic-and-metal device. A gentler power source now used to pump the heart may be helping, he said.

No date has been set for a move back to Jasper.

DeVries said he is eager for his next experimental implant -- the fifth in his federally approved series of seven -- but no candidate has met strict eligibility requirements. Patients must, for example, have strong family support, live near Louisville and be dying with no other medical option, such as a transplant.

Rapid advances in transplant techniques have caused that last category to dwindle. During the last six months, transplant centers nationwide have raised their age limit from about 55, thanks to new evidence that older patients can benefit from such procedures, said Dr. Allan M. Lansing, chairman of Audubon's heart institute.

Lansing acknowledged last month that Murray P. Haydon, who in February received an artificial heart at age 58, would now be "more seriously considered" for a transplant.

Haydon, now 59, had been described as too old for a transplant. But in July, Audubon surgeons performed a transplant on Lowell Boggs, 59, of Cincinnati, whose condition was "perhaps very similar" to Haydon's, Lansing said.

Haydon has spent nearly half a year in intensive care, suffering bleeding problems, a transient stroke, pneumonia, infections and respiratory difficulties requiring intermittent use of a ventilator.

Boggs was discharged last week to the Humana-owned apartment building where Schroeder today became his downstairs neighbor.