Three Northern Virginia jurisdictions will receive increases ranging from 27 to 40 per cent in cash payments they get from federal revenue sharing during the fiscal year that begins Oct. 1, The Washington Post learned yesterday.

The District of Columbia and Montgomery and Prince George's counties will receive much smaller increases in federal payments during the same period.

The Treasury Department is expected next week to begin notifying thousands of state, county and municipal governments of their fiscal 1978 revenue-sharing "entitlements."

Revenue sharing is a federal program that returns to about 39,000 governments $6.85 billion a year in federal tax receipts that the localities can spend as they wish, within certain broad limits. Congress last year extended the program through Sept. 30, 1980.

The amount of money a jurisdiction is entitled to is based on a complex formula that takes into account, among other things, per capita income, local tax burdens and population.

According to figures compiled this week by the Treasury Department, Arlington County, which received $1.85 million in federal revenue sharing in fiscal 1977, will get $2.47 million in fiscal 1978, about a 36 per cent increase.

Fairfax County will see its cash payment grow from $5.265 million in fiscal 1977, to $6.701 million in fiscal 1978, about 27 per cent more.

Alexandria will receive a revenue-sharing allotment of $2.192 million in fiscal 1978, up 40 per cent from the $1.565 million in fiscal 1977.

Most state and local governments have different fiscal (or spending) years than does the federal government. The federal government closes its books on Sept. 30, which most local governments close their books on June 30.

Revenue-sharing funds are important to state and local governments, most of which are strapped for cash, but they represent only a small por tion of the overall budgets of such governments.

While Northern Virginia jurisdictions will receive big increases in federal cash payouts, the District's share will go up only 3.8 per cent, from $28.818 million next year.

Montgomery County's revenue-sharing payments will rise 2.7 per cent, from $8.073 million to $8.294 million.

Prince George's County's revenue sharing allotment will rise from $12.784 million in the current fiscal year to $13.2 million in fiscal 1978, an increase of 3.2 per cent.

Some local governments in Montgomery, Prince George's and Fairfax counties receive their own revenue - sharing payouts. In Prince George's County, municipal governments will receive another $1.054 million next year; local governments in Montgomery County will get $602,212, and another $231,535 in revenue-sharing funds will go to local governments in Fairfax County.

The localities will be informed of their payouts next week. Treasury officials said, and may protest the size of their allotment if the factors the agency used in computing the entitlements are incorrect. Treasury used the latest data out of the Census Bureau to update population and per capita income figures.

Fairfax County's increase was large partly because the government withdrew $1.9 million in revenue sharing last year, claiming that it had overpaid Fairfax County in earlier years. Similarly, Arlington's allotment in the final months of 1976 was reduced because of overpayments.

While D.C. may not have fared as well as some of its Northern Virginia neighbors, it did better than Chicago. According to rough calculations by the Treasury, Chicago's revenue-sharing funds will go up only 1.5 per cent, from $80 million to $8.15 million.

Plains, Ga., the home of President Carter will receive lower revenue-sharing funds next year. Treasury has reduced the Plains allotment to $13.883 from $15.460. Treasury did not say why, but the town did lose five of its 633 residents this year.