A sharp increase in the number of unemployed persons in Washington's suburbs pushed the metropolitan-area unemployment rate to 4.0 percent in December, its highest level in six years, according to figures released yesterday.

Unemployment in the District fell significantly, from 6.9 percent in November to 6.5 percent. But officials said the drop mostly reflected Christmas-season hiring, not a turnaround in the troubled economy.

Christmastime hiring in the entire area was only about half what it has been over the last five years. From September to December 1990, 10,800 jobs were added in the retail trade, according to Richard Groner of the D.C. Department of Employment Services, which compiles the area statistics. Over the previous five years, the average increase in jobs during the same period was 21,000.

In Maryland, which also released its unemployment rate yesterday, joblessness went up from 5.3 percent in November to 6.0 percent in December. Officials of the state Department of Economic and Employment Development said jobs were lost in the construction, auto-manufacturing, restaurant and hotel sectors, among others.

The Virginia unemployment rate, released earlier this week, was 4.9 percent in December, up from 4.5 percent the previous month.

The 4.0 percent unemployment rate for the metropolitan area still is lower than the comparable 5.9 percent rate for the nation as a whole. (Unlike the U.S. figures, the local employment statistics are not adjusted for seasonal variations.) But there were other signs that the region's recession has not abated.

Between December 1989 and December 1990, for instance, 15,000 jobs were dropped from area payrolls, based on a survey of employers. In the mid-1980s, by contrast, the region was adding more than 100,000 jobs a year. The survey of households, which provides the unemployment data, showed that the number of unemployed suburban residents rose 75 percent over the last 12 months; for the area as a whole the increase was 64 percent.

Anecdotally, business officials said they see no sign of an upturn. At the Washington headquarters of Russell Reynolds, an executive-search firm, phones ring constantly with queries from executives seeking work. Fewer corporate clients are hiring at the moment, they say.

"Our secretaries explain hundreds of times a day that we can't schedule a meeting {with the would-be applicant} until we have something to talk about," said John Franklin, managing director of the office.

The job losses for the area would have looked worse without a significant increase in state and local government jobs over the last year of 7,100. The private sector lost 22,000 jobs in the same period.

Experts predict that the government sector will begin losing jobs soon because many local jurisdictions have announced hiring freezes and one -- Prince Georges County -- has actually laid off workers.

"That's probably the next shoe to drop," Groner said about the government sector.

He pointed out, however, that even if the local economy was not improving, there was little sign in yesterday's figures that it was getting worse. The annual job loss, at 15,000, was about the same as the job loss from November 1989 to November 1990 of 14,800.