A sign on the door of the Capitol Courts Club in Sterling tells prospective tennis students to "see Judi for details."

Right next to the sign was another, more ominous one yesterday, imploring anyone with information about the whereabouts of Judith L. Demaria, the club's tennis pro, to contact the Loudoun County sheriff's department.

Sheriff's deputies and volunteers -- sometimes as many as 100 -- yesterday continued their search of the area around the Washington and Old Dominion bicycle path, where Demaria, 27, was last seen, for clues to her whereabouts. On Saturday they found "a substantial amount of blood," according to Deputy Sheriff Robert E. Turner.

"We found some blood off the bike trail," said Turner, who said laboratory tests showed it to be human blood. "We're going to start searching again from where we found the blood."

Turner said the blood, which still was being analyzed, was found in the general area where Demaria was last seen, near Broad Run bridge.

According to accounts by sheriff's deputies, Demaria left the club about 11:30 a.m. Friday, her usual routine three times a week, to jog along the W&OD bicycle path. A park ranger saw Demaria, dressed in blue terry cloth shorts and a navy blue top, as she approached the bridge. No one is known to have seen her since.

Yesterday, under a blazing August sun, deputies stopped the occasional joggers, bicyclists and walkers along the asphalt bike path to inquire whether they had been on the path about the time Demaria was last seen.

Officers handed out flyers that described Demaria as 5-foot-6, 140 pounds, with black hair and brown eyes.

Turner said deputies had been joined in the search by members of the Appalachian Search and Rescue Conference, Sterling Volunteer Fire Department, Loudoun County Rescue Squad, Dogs-East, Loudoun County REACT, Round Hill Rescue Squad and the Sterling Ruritan, a civic group.

He said family members, who "were out as long as I was," had been told of the discovery of blood. "We were so far into the search that the family kind of expected anything," he said. "When you have a real responsible girl who doesn't show up, you kind of expect the worst."

Dan Weaver, Demaria's brother-in-law, said in a telephone interview yesterday that Demaria's father, stepmother and sister declined to be interviewed.

Rose Marie Croce, 20, an employe at the Capitol Courts Club at 308 Glenn Dr., said Demaria played on the George Mason University tennis team when she was a student there. She lives alone in Manassas and is a Nautilus instructor as well as a tennis pro, Croce said.

In addition to her Capitol Courts classes, Demaria also teaches a fitness class at St. Timothy Catholic Church in Chantilly and tennis lessons at the Fairfax Racquet Club.

"Judi got along with everybody," said Lisa Smith, 20, who also works at the club. "We're not just saying that."

Croce said she saw Demaria leave the club on Friday to go jogging, which she did every Monday, Wednesday and Friday. Demaria told her she'd be back at 12:30.

But Demaria, who friends said was always punctual and would call if she was going to be even five minutes late for work, did not return on time, and Croce said she began to worry. "I went on my bike toward Herndon a couple miles," she said. "I was asking people if they had seen her, but there was no sign."

The club called the sheriff's department at about 3 p.m., she said, and her family at about 5 p.m. Demaria's car was still at the club.

Croce said she and about 10 to 20 other people went to the bike trail, formed a line and called out her name to no avail.

Lt. Leonard W. McDonald said the search, which was scaled down yesterday, covered about 1,000 yards on both sides of the path for about 1 1/2 miles.

The path, which also accommodates horseback riders and parts of which were recently covered with asphalt, stretches from Alexandria to Purcellville.

Turner appealed to anyone with information concerning Demaria to call (703) 478-1086 or (703) 777-4791.