The battle to maintain the nation's flood insurance program with private-sector insurers rather than as a "federalized" plan is being waged down to the Dec. 2 deadline.

Lobbyists for the current operators, the National Flood Insurers' Association, have instigated a congressional, industry and employee letter-writing campaign which has deluged President Carter and Housing and Urban Development Secretary Patricia Roberts Harris with pleas to delay action on the plan until Congress reconvenes in the new year.

The flood program has provided insurance for 1.2 million homeowners and businessmen located in floodplain areas throughout the U.S. since 1969.

About 165 area residents whose jobs at NFIA's large computer operation in Arlington are threatened joined the effort last week, taking their case to key congressional offices.

In a three-page letter to Sen. William Proxmire (D-Wis.) and ranking House members, the employees charged that the only issue considered in the shift to a new program operator was cost, not the quality of the program administered by NFIA.

Twenty-two members of the Senate Banking and Governmental Affairs Committees and the House Appropriations and Banking committees dispatched letters to Carter and Harris within the past two weeks, calling for a delay until the General Accounting Office can complete a review of the proposed budgets of NFIA and the designated new operator. EDS Federal Corp. of Dallas. EDS is owned by Texas multimillionaire, H. Ross Perot.

Among those asking for the delay are Sens. Abraham Ribicoff (D-Conn.), chairman of the Governmental Affairs Committee Thomas Eagleton (D-Mo)., chairman of the Governmental Efficiency Subcomittee Henry Byrd (Ind.-Va.) Russell Long (D-La.); Bennett Johnson (D-La.); Harrison Williams Jr. (D-N.J.); Edward Brooke (R-Mass.); John Tower (D-Tex.); Robert Morgan (D-N.C.); Jake Garn (R-Utah); Richard Lugar (R-Ind.); H. John Heinz Ill (R-Pa.); and Harrison Schmitt (R-N.M.)

The most prominent senator to oppose a delay in Proxmire, who supports HUD's view that the EDS-operated program under HUD oversight would save $15 million a year compared with NFIA.

The alleged $15 million saving and the manner in which HUD officials have handled the negotiations for the 1978 flood program are the real issues in the lobbying campaign, Hill sources said.

As Sen. Williams wrote to Harris, "I am especially concerned about the timing and manner of the Department's notice to the Congress. Because adjournment is imminent, the Department's notice to Congress was furnished under circumstances which preclude even the most cursory considerationof the important issues at stake."

HUD's general counsel, Ruth Prokop, insists that the department has to complete the contractual details with EDS under the timetable prescribed by statute - which would allow the signing of the final agreement on Dec. 2. The department opposes further delay because it would jeopardize an orderly transition from NFIA to EDS when NFIA's operation of the program ends Dec. 31, she explained recently.

As a result, the last-minute lobbying campaign is seen is futile by HUD officials. Prokop said only a joint congressional resolution barring Secretary Harris froms signing the contract with EDS would hold up the timetable.