When Ballou High School teacher Joan Pierotti went on strike Tuesday morning her mortgage payment was already a month overdue.

But Pierotti, who supports three children with take-home pay of $448 every two weeks, says she decided to walk the picket line as an "act of principle," even if it means she has to take out a loan to pull her family through crisis.

Anacostia High School teacher Pat Campbell and her three children were "experts in penny-pinching" even before the strike, she said, and they have now decided to delete meat from their diet as a further economy measure.

Washington Teachers Union leaders urged striking teachers yesterday not to express their financial woes publicly because that might be taken as a sign of weakness.

But Pierotti, Campbell and many other teachers walking yesterday's picket lines were unaware of the edict and willingly -- although often anonymously -- answered reporters' questions about the growing strain on their family budgets.

"It's no secret that most of us like other people live up to every penny of our income and beyond," said one high school teacher, whose teacher-husband is also out on strike. "But supporting that strike is very important to us. We talked it over and decided to strike even if it meant not paying some bills."

William H. McBride, a drivers' education teacher at Ballou High School, has been expecting a strike for the last three or four months, he said. In preparation, McBride said he managed to save enough money to make one house payment in advance.

"I'm not saying how long I'm prepared to be on strike," he said. "But I do have one mortgage note paid and I'm willing to borrow money to keep going, if necessary."

Pierotti, who has taught in the D.C. public schools for 10 years and has a master's degree, earns $19,000 a year. After seven additional years of teaching and either a doctorate or 60 more graduate school hours, she could be paid as much as $25,000, the maximum salary for D.C. classroom teachers.

The District's top salary of $25,000 -- for a teacher with 17 years' experience and a master's degree -- is the third highest of area school jurisdictions, according to a comparative guide prepared this school year for the Metropolitan Area Boards of Education.

Alexandria's top figure is $25,972, and Fairfax County's is $25,511 -- in both cases, for a teacher with 20 years' experience and a doctorate. Arlington County pays a top salary of $24,786 for 14 years' experience and a dectorate. Montgomery County's top salary is $23,681 for 28 years' experience and a master's plus 30 additional study hours. In Prince George's County, the top salary is $24,591 to a teacher with a doctorate and 25 graduate hours.

But the D.C. public school system pays the area's highest beginning salaries of $11,824 for a teacher with a bachelor's degree and $13,008 with a master'.

Arlington County's beginning salary, for a teacher with a bachelor's degree and no experience, is $11,296. In Alexandria, the comparable figure is $10,601; in Fairfax County, $10,500; in Prince George's County, $10,897, and in Montgomery County, $10,479.