A full shift of 20 Annapolis firefighters reported to work yesterday, apparently abandoning a "sick-out" protest that had left Maryland's capital with minimal fire protection over the holiday weekend.

"There are two ways to look at why they came back," said John C. Apostol, the mayor of Annapolis. "Either the mysterious epidemic is over, and everyone's well, or the men who were sick for the Saturday shift could not come up with doctor's certificates to prove they were really sick."

Apostol explained that city firefighters are allowed to miss one shift without excuse, but for a second absence they must produce a written doctor's report explaining their illness. Most of the 20 firemen who returned to work yesterday were among those who called in sick on Saturday.

The "sick-out" began Friday when contract negotiations between the city and its firefighters' union stalled. The city offered a 5 percent salary increase, but the firefighters were demanding a 7 percent raise.

On Monday, when only 5 of the 18 scheduled firemen reported for duty. Douglas A. Remaley, president of the Annapolis Fire Fighters Local 1926, insisted that the low attendance did not represent a sickout."

"There is no sanction job action or slowdown," said Remaley. "As far as I'm concerned, if the men call in sick, they're sick."

Apostol said that he expected the contract talks to resume tomorrow.