Tax collections by metropolitan Washington's six largest cities and counties grew almost twice as fast last year as government spending, a pattern that is not likely to be repeated, a business-sponsored research group reported yesterday.

The D.C. Municipal Research Bureau said tax collections in the region increased 14.8 percent in fiscal 1977, compared with 1976, while spending increased 8.1 percent to a record total of $2 billion.

"It is unlikely that the combination of such rapid revenues growth will be duplicated in future years," the bureau said. "The more normal pattern will be for both to grow at about the same annual rate."

The bureau, an independent nonprofit organization financed largely by Washington business groups, did not attempt to forecast the growth rates. Its 11-page report looked back at fiscal 1977 and concluded that area governments were financially healthier than they had been in 1976.

The report made no attempt to compare the total tax burden of District of Columbia or suburban residents, or the per capita cost of local government.The D.C. government would be far out in front in any such comparison, since it provides many services that suburbanites get from the states of Maryland and Virginia and from such bodies as sanitary districts, the report said.

However, the report does not provide some guideposts for taxpayers who want to see how the growth of their burdens compares with that of residents elsewhere in the region.

The bureau said every major area government kept its increased spending last year below 10 percent except Fairfax County, where expenses increased by 12.8 percent.

Real estate tax collections the largest source of income for the suburban governments, increased 24 percent in Fairfax County, about twice the rate for all the other cities and counties. Areawide, real estate taxes yielded $781.6 million in 1977, up $685.3 million the year before.

The report spells out the high dependency of the suburbs on real estate taxation, demonstrating why taxpayers are resisting increases to pay for such items as the rising cost of running the Metro transit system.

Just a week ago, the Virginia General Assembly narrowly defeated a proposal to levy an increased sales tax in the Washinton suburbs, with its income earmarked for Metro.

Alexandria yesterday joined the District of Columbia and Montgomery County in proposing a reduction in the real estate tax rates in their fiscal 1979 budgets. Proposed budgets in Fairfax and Arlington counties would hold the tax at current levels.

The real estate tax pays only 15 percent of the District of Columbia's cost of operations, compared with 70 percent in Fairfax County, 62 percent in Arlington County, 57 percent in Alexandria, 54 percent in Prince George's County and 51 percent in Montgomery County.

The D.C. government's biggest revenue source is income taxes, which are levied by the two adjacent states and not by local governments.

On the other hand, the actual dollar burden of real estate taxes was, on the average, higher in the District of Columbia than in the suburbs.

The average city taxpayer paid 2.04 percent of the value of his property in real estate taxes last year, compared with a range from 1.33 percent in Montgomery County to 1.92 percent in Fairfax County.

"While citizens have been protesting about property taxes," the report said, "there has been an excellent record of payment with a minimum amount of delinquency in property tax payments." Collections ranged from 95.8 percent in Alexandria to 99.3 percent in Montgomery County. The D.C. collections totaled 98.4 percent.

The report noted that the total value of real estate for tax purposes is greater in three countries - Montgomery, Fairfax and Prince George's - than it is in the District of Columbia. Montgomery was highest, with a $12.1 billion valuation, while the District totaled $8.2 billion.

Contrary to a widespread public notion, the report indicated that the local jurisdictions are having no apparent difficulty making their annual payments on long-term debt for construction programs. The debt last year totaled about $2.4 billion.

In the suburbs the debt for the most part, takes the form of bond issues. In the District of Columbia, the money was borrowed from the U.S. Treasury.

Of the six governments, Alexandria spent the highest proportions of its budget - 13.1 percent - on debt payments. Arlington County spent 12.1 percent, Fairfax County 10.9 percent, Prince George's 7.9 percent, the District of Columbia 7.2 percent and Montgomery County 5.5 percent.

The report said the District's debt increased 14 percent last year, the largest rise in the region, the result of a continuing 10-year, $1.6-billion program mainly of replacing old public facilities.

However, two of the biggest chunks of debt in the region were not included in the $2.4 billion total listed in the report.

One is $997 million in bonds floated by Metro, which were supposed to be paid off from future fare collections, but cannot be. The other is $2 billion in unfunded pension liabilities owed retirees by the District of Columbia. Legislation to ease the pension burden is pending in Congress, but the Metro bond question remains unresolved.

The D.C. Municipal Research Bureau has its office at 1612 K St. NW. Its executive director is Philip M. Dearborn.

Following is a summary of the increases in general fund revenues (mainly taxes) and spending in 1977, compared with the previous year: