Partly because $7 million in taxes on the estate of Marjorie Merriweather Post were paid all at once, a congressional subcommittee was able this week to cut the federal payment to the District of Columbia goverment by a somewhat larger amount.

The House District Appropriations Subcommittee, acting on the city's proposed budget, voted to recommend to Congress that $8.7 million be trimed from the support the city sought from the U.S. Treasury. A few small cuts in the budget also were made.

Subcommittee Chairman William H. Natcher (D-Ky.) mentioned the $7 million that the city collected from the estate of Mrs. Post, heiress to the Post cereal company fortune, who was a Washington resident. When Mrs. Post died in 1973, her estate was estimated at $117 million.

City officials said her heirs paid the estate taxes in one chunk in this fiscal year, giving the city a $7 million windfall.

Before that became known, the city made two requests for federal payments to Congress. It asked for $4 million to help pay for a few leftover items it wants to add to the current 1977 budget. It also asked for the full $300 million payment authorized by federal law to support the pending 1978 budget of $1.4 billion.

The subcommittee refused the $4 million for 1977 and cut the payment for 1978 to $295.3 million - $4.7 million less than the city's request. Natcher said the $4.7 million would be left for a possible later emergency.

Although the 1978 payment cut is less than the District often has suffered, criticism was heard at the District Building.

"Such action shows an insensitivity in Washington's financial needs . . . A strong case can be made to double the federal payment to $600 million rather than slashing it by (nearly) $5 million." City Council member Marion Barry (D-at-large) said in a statement.