The land of milk and honey and money is in the suburbs of Washington but District residents "are having one of the biggest problems in the nation coping with inflation and economic stagnation," says a new report by Sindlinger's Economic Service.

"A haven of economic tranquility, the suburbs of the nation's capital are enjoying a life-style that appears to be almost immune from the problems of inflation and recession that are plaguing most Americans," the special survey of 1,280 area resident concludes.

More than half the Washington suburbanites interviewed experienced income gains in the last six months, while two of three expect their own income and area business in general to improve by next October.

In the District, however, residents "are most pessimistic about future job opportunities, unlike their suburban friends." Only 25 per cent of city residents reported income gains over recent months. Three out of four District residents expect area business to remain about the same or to decline between now and next October.

Sindlinger's, which is based in Media, Pa., has been conducting public opinion surveys for 28 years. Each week, the company reports on its sampling of opinion in every state and large economic market through daily telephone surveys of consumers.

The unusual survey of one market, metropolitan Washington, was conducted during the 56-day period from Feb. 9 through April 6. Two Sindlinger interviewers suggested the D.C. area report because they "observed during January how the confidence levels in the Washington suburbs, where many of the government's top policy and decision makers live, consistently ran far ahead" of opinion surveys in all parts of the United States.

In assessing results of the 56-day survey here, Sindlinger's told its clients: "If everyone lived in the suburbs of Washington, D.C., the nation would be enjoying an economic boom - its greatest in history."

Residents of the "unique enclave embracing sectors of Maryland and Virginia bordering the capital form a select corps of consumers that has been almost immune, and to a large degree isolated, from the financial ravages caused by the nation's economic problems in recent years," according to the report.

But, while the suburban affluence contrasts with most other sections of the nation, it clashes "most sharply with the District of Columbia which it surrounds . . . these findings gave the Washington suburbs an economic glow that was characteristic of Sindlinger findings in the Deep South during the go-go years of the 1960s," the report states.

Among major findings from the Washington study:

Only 1 of 12 suburban households suffered an income decline in the past six months.

Only 1 in 25 expects a decline in employment in the D.C. area over the next six months.

In the District, 32 per cent reported a decline in income over the past six months and 42 per cent said their income was unchanged.

Among D.C. residents, 38 per cent reported a positive level of "household money supply" for spending, one of the lowest levels in the U.S. In the suburbs, the positive level was 69 per cent compared with a 54 per cent national average.

The Sindlinger report says nationwide consumer confidence increased slightly for the week ended April 13, but the gain took place before President Carter abandoned his $50 tax rebate plan. The report says some of the increased confidence reflected anticipation of getting the money.

At the end of March, seven of the most populous states were above national averages for consumer confidence, led by Georgia. The outlook in Florida was poor because winter weather hurt tourism and agriculture. The 15 largest metropolitan areas generally trailed national averages in the consumer confidence surveys.