Officials in suburban Maryland successfully scrambled this week to secure fluoride for the area's drinking water in the midst of a national shortage, the first in more than 10 years, of the chemical that inhibits tooth decay. That shortage has hit a handful of cities across the country and left much of the Baltimore area without sufficient supplies of the chemical.

Officials of the Washington Suburban Sanitary Commission, which had depleted its fluoride supply last week, said they expected to receive a full shipment yesterday from a new distributor, St. Louis-based Chemtech Industries Inc. They said they expected to have enough fluoride to ride out the shortage, which is expected to last a month and was prompted by a slump in the use of phosphate fertilizer. The chemical used for fluoridating water in this area is a byproduct of the production of such fertilizer.

The WSSC had depended on another distributor, LCI Ltd., to supply fluoride for the 1.3 million people using the water system in Montgomery and Prince George's counties. But that distributor, which also supplied the Baltimore water system that serves 1.6 million people there, ran out of the chemical.

Two water plants in northwest Baltimore that supply the city, Baltimore County and parts of Howard and Anne Arundel counties were out of fluoride yesterday, water officials there said. A third plant, located in the northwest section of the city, had a one-week supply, they said.

The District of Columbia water supply is unaffected by the shortage, according to representatives of the U.S. Army Corps of Engineers. Northern Virginia is also unaffected, according to the Centers for Disease Control in Atlanta.

Health officials said the lack of fluoride in the water would have to last six months to a year to have any measurable effect on the prevention of tooth decay.

WSSC representatives began negotiating with Chemtech about a month ago, a company representative said yesterday, and so far is the only water system to receive extra chemicals from the company during the crunch.

Officials of the National Fertilizer Center of the Tennessee Valley Authority in Atlanta linked the fluoride shortage to a drop in the export market for phosphate fertilizer.

Countries such as Tunisia and Jordan, which once relied on the American market, have developed their own methods for producing the fertilizer and have increased their share of the world market by 6 percent during the last year.

At the same time, use of the fertilizer in the United States has steadily dropped since 1979 -- from 5.6 million tons to 4.6 million tons -- and is expected to continue to drop, according to analysts.

So far, five cities, including San Francisco and Cincinnati, have depleted their fluoride supplies, according to the Centers for Disease Control, and two others -- Baltimore and Philadelphia -- are expected to be without the chemical by next week.