The D.C. City Council, in an unexpected action, gave preliminary approval yesterday to Mayor Walter E. Washington's plan to keep the police department at the 4,141-member level insisted upon by Rep. William H. Natcher (D-Ky.).

The full council membership, sitting as a budget committee, endorse the mayor's request to add $2.4 million for the police to a proposal supplemental city budget for the 1979 fiscal year, which begins next Oct. 1. The action was recommended by Council Chairman Sterling Tucker.

That money would be enough to keep the police department from shrinking by 264 officers.

Council member Marion Barry (D-At Large) said her would seek to trim the police fund when the council considers the supplemental budget again at a legislative session April 4. He said he wants to avoid any need to fire any newly recruited officers.

Tucker and barry have both announced their Candidacies for mayor. Washington is expected to seek reelection, but has not announced his plans.

The police issue has divided the mayor and council for more than two position that the size of the police years. The council has prevailed in its force should be reduced as officers retire of resign. barry said the city is now safer than when it had and even larger force.

Howere, Natcher, the influential chairman of the House D.C. Appropriations Subcommittee, has insisted on keeping the force at its authorized strength of 4,141, and has provided funds to do so.

Mayor Washington told the citys new police chief, Burtell M. Jefferson, to use some of the money to replace retiring officers. Jefferson has taken steps to hire 54.

Last week, Jefferson testified at a council hearing in favor of the mayor's request for $2.4 million. The proposal encountered sharp critism, chiefly from Council member David A. Clarke (D-Ward 1). It was generally beleived the council would cut the funds.

Yesterday, howere, Tucker recommended suppot for the mayor's request. He told a reporter that crime is a "primary public concern," and that he did not want to create morale problems for the new police chief.

In a series of committee actions yesterday the council added slightly more than $1 million to the mayor's supplemental budget requests for $27.3 million more in fiscal 1978 and $25.9 million more in fiscal 1979. All votes are subject to the April 4 meeting.

Major additions recommended by Tucker included $150,000 for printing the Municipal Code of Local laws and regulations; $250,000 toward a payment of $480,000 to Robert J. Pierce, a volunteer worker who was serioulsy wounded in the Hanafi Muslim take-over of the District Building last year, and $100,000 for programs of the commission on the Arts.

On the recommendation of council members Barry and William Spaulding (D-Ward 5), the proposed arts funding was raised to $300,000.

The subsidy for school children's transit rides from $4.3 million to $4.5 million on recommendation by Jerry A. Moore (R-At Large) in anticipation of extending the subsidy from buses only to Metrorail.

Douglas E. Moore (D-At Large) won approval of a $75,000 fund to pay the tuition for veterinary medicare students from the city. He urged that an arrangment be made for the students to attend classes at Tuskegee (Ala.) Institute.