A House subcommittee yesterday approved a bill to designate the third Monday of January as a national holiday, starting in 1986, to commemorate the birthday of slain civil rights leader Martin Luther King Jr.

The bill was a compromise of legislation introduced by Rep. John Conyers (D-Mich.) to designate Jan. 15 as the legal holiday and to make it effective immediately. Conyers has offered the measure in every Congress since King's assassination in 1968.

The measure approved yesterday by a 5-to-1 vote of the House Post Office and Civil Service Subcommittee on Census and Population was introduced by subcommittee Chairman Katie Hall (D-Ind.).

Some members of Congress had expressed concerns about the cost of the holiday to the federal government and to business in terms of time lost at work. A cost analysis showed that a Monday holiday would not be as costly as one that could fall on any day of the week, a subcommittee staff aide said.

The full committee probably will act on the bill after the July recess, the aide said.

Conyers was not displeased with the alternative approach, according to a Conyers aide, who said the delay in the effective date of the holiday was intended to dampen criticisms that the costs cannot be borne during the current recession.

"The assumption is . . . that the country is in such economic straits that we need two years for the economy to revive, and this will have less fiscal impact," he said.

The panel rejected a proposal by Rep. William Dannemeyer (R-Calif.) to make the third Sunday in January a day of prayer and remembrance.