Michael Sullivan, a 29-year-old troubleshooter for Potomac Electric Power Co., works the midnight shift as a "mobile operator," answering calls to fix downed power lines, damaged transformers and other high-voltage malfunctions.

But after seven nights, Sullivan switches to a 3 p.m. to 11 p.m. shift for a week. Then, he switches to a daytime shift for a week, then midnights. Then he is back to the 3 p.m. shift -- the one in which he doesn't see his wife and two children during their waking hours.

The rigors of constant "rotating shifts" -- which are required of about 25 percent of Pepco's unionized work force -- can seriously disrupt family life and physical health, according to union experts. And the problems of rotating shift work are among the key issues in the current strike that is the first in the 89-year history of the giant utility.

The walkout by 3,300 members of the International Brotherhood of Electrical Workers was sparked by a number of issues, including a proposed cut in health benefits and concerns about pensions and wages. But the constant 24-hour-a-day, 365-day-a-year demands of providing power to 1.75 million Washington area residents adds extra tension to the dispute.

"The problem is not money. We make good money. But there are hardships on this job that affect your body. Your family, your kids, everything," said Sullivan, a nine-year employe who earns $15.26 per hour on a work schedule that he said causes near-constant fatigue and other irritations in his Wheaton household.

"By the time I get home, my wife and the kids are asleep. When they're up, I'm asleep . . . . Then it all changes," he said. Sullivan said the schedule is sometimes toughest on his son, Michael, 8. "I see behavioral differences," he said. "He is harder to control when I haven't seen him for a while. His teachers at school even notice a difference in his behavior. And each time, it's when I'm not around."

Sullivan said the constant rotation also makes it very difficult to arrange child care, and such troubles contributed to his wife's recent decision to leave her job as a bookkeeper. "It is tough on everybody," he said.

Federal mediators will attempt to resolve the strike issues at a bargaining session today.

Pepco, meanwhile, reported outages yesterday affecting some 3,000 homes in the District and Maryland, but most were restored quickly by management crews working midnight shift to repair damage from an early-morning storm. The only longer outage affected about 200 homes in Rockville that were without power for three hours, Pepco said.

Picketing at 11 Pepco sites continued for the third day yesterday. D.C. police reported a picketer was injured just after midnight when he was hit by an unmarked police car outside a Pepco plant in Northeast. The incident is under investigation.

Among the toughest issues to be discussed at today's mediation session is IBEW's demand that Pepco limit rotating shifts and increase premium pay required of men and women who must alter their schedules, often on short notice. Pepco currently pays 50-to-55-cent hourly differentials on night shifts. The company has offered 65 cents. But IBEW says that Pepco is enjoying record profits and can afford to pay a $1 hourly premium and hire extra staff to curb the practice.

Pepco officials yesterday would not discuss shift work or other issues, saying they did not want to jeopardize pending negotiations. But company officials have said they presented a "fair and reasonable" package of proposals, including increased differentials and a three-year wage increase of more than 13 percent. Pepco said it regretted what it called "an uncalled-for" strike.

John Zalusky, an AFL-CIO labor economist who monitors collective bargaining, said that complaints about shift work are among the most difficult to resolve because they involve social and psychological problems for workers balanced against economic concerns for companies.

"It's a lot like constant jet lag," said Zalusky. "Night shift is rough, but constant rotating shifts are the worst, because the body never fully adjusts."

Terry Cross, president of IBEW Local 1900, said the nearly 800 rotating and night-shift workers are particularly irritated by Pepco's recent addition of "quasi-shifts" with irregular starting times and by the company's failure to give longer notice of shift changes. Union members filed more than 50 grievance cases on shift changes under the expired three-year contract, he said.

"It's like 24-hour guard duty. Somebody's always got to be on," said Terry White, a 15-year veteran who rotates shifts as a power plant operator.

White said normal fatigue is worsened by frequent emergency calls.

"You got nights and you got days. And then you get a 2 a.m. call to come in. You got no personal life," he said.

Cross said, "It's one thing to know your schedule ahead of time, but somebody can say to you 'Guess what? You have to work.' And you may have tickets to a ballgame or a family picnic planned. The company should minimize this."