D.C. Tax Assessor Donald Beach told the Federation of Civic Associations last week that for the first time assessment inspectors will attempt to enter every District home to make assessments.

Before this year, Beach said, inspectors actually entered only 15 percent of the homes prior to determining assessments.

"We know that you are often working during the hours our inspectors are usually working," explained Beach, "so we are going to let some of our inspectors work on Saturdays and change their schedules so they can work at night."

Beach also said homeowners who own vacant land adjacent to their homes should file a document with the assessor's office so the vacant land will be assessed at a lower rate.

The District tax assessor also urged senior citizens to claim an income tax property credit, which he said many are not using to their advantage.

The Washington Cathedral Flower Mart will be from 11 a.m. to 6 p.m. tomorrow on the grounds of the National Cathedral, Wisconsin and Massachusetts avenues NW. Admittance is free.

Proceeds from the sales will be used for maintenance of the cathedral grounds and to pay salaries of students from Phelps Vocational School who work as apprentice gardeners under the supervision of the cathedral staff.

Elizabeth Taylor Warner is expected to officially open the show.

Three Washington students are among the more than 1,900 high school seniors who have won college-sponsored, four-year Merit Scholarships, according to an announcement by the Natiional Merit Scholarship Corporation.

The scholarships are renewable for up to four years of undergraduate study and are offered with the stipulation that they be used at the sponsoring institution. The average annual stipend is about $700, depending on the winner's financial circumstances.

The D.C student winners are: Louise E. Sivak, 4525 brandywine NW, of Sidwell Friends School, from Wesleyan University; Magaret A. Willens, 3307 Newark St. NW, of Sidwell Friends School, from Wesleyan University, and Sean T. Enright, 9804 Ashburton La., of Bethesda, from Northwestern University.

The D.C. Department of Recreation's cooperative pre-school play program will hold an open house and pre-registration for the fall term the week of May 14 at all of its area centers.

District children from 3 to 5 years old may be registered from 9 a.m to 9 p.m. weekdays through May 18. Proof of birth should be submitted by the parent or legal guardian.The pre-school program begins in September. For information on registration locations, call 576-7278.