An official of Action, the government's volunteer agency, has sent a letter to 46 state offices of Birthright, an antiabortion organization, urging their 500 chapters to apply for federal funds earmarked for antipoverty activity.

The letter was sent under the federal frank but on plain white stationery and signed by Myron E. McKee, special assistant to the executive officer of Action. It offered advice on how to apply for "paid Vista volunteer positions." Vista (Volunteers in Service to America) is a division of Action.

Action spokesman Jim Malone said the letter was "beyond the bounds of McKee's authority."

McKee has been informed in writing that he acted without authority and "will be expected to reimburse" Action for the $150 he spent on the use of the postage frank, Malone added.

McKee told United Press International that he had acted legally in sending the letters, but declined to comment further. He did not respond to calls from The Washington Post.

Word of the letter has further fueled the continuing hostilities between the agency's Republican management and adversaries on and off Capitol Hill.

Rep. George Miller (D-Calif.), for 10 years a member of the House Education and Labor Committee with jurisdiction over Action and Vista, said the incident is "more serious than the misuse of the frank. . . . It shows a total disregard for the mission of Vista and the guidelines under which that organization is supposed to operate."

The guidelines requiring that Vista funds be spent on antipoverty activities were "restated as recently as the last Congress because of violations of the law by this administration," Miller said. "Congress said very clearly it wanted Vista to work on programs devoted to hunger, homelessness, illiteracy, unemployment . . . . And it's also in violation to provide preferential treatment to any group."

Any responses to applications coming as a result of the McKee letter "are suspect, and we'll certainly watch that," Miller added.

"In my view there are serious questions about the legality of the mailing and serious questions regarding the appropriateness and legality of assigning Vista volunteers to organizations such as Birthright," said Mimi Mager, executive director of the Friends of Vista, a bipartisan organization co-chaired by Sargent Shriver and George Romney that has sought to save Vista from extinction. "The real problem is the diversion of antipoverty resources."

The package McKee -- an unsuccessful Republican antiabortion candidate for a congressional seat in Minnesota last year -- sent to the Birthright offices included application materials, a model application filed successfully by a Massachusetts Birthright affiliate, and nine "pointers" on how to apply for "paid Vista volunteer positions."

The Massachusetts program currently is the only Birthright activity funded by Vista, Malone said. Its funding includes about $100,000 for a staff coordinator and a dozen volunteers.

"Each state should apply for at least 10 paid Vista volunteer positions," the letter said. "Each separate office in a state (say seven) may apply for three Vista volunteers."

The letter also promised a response in what critics say would represent record time. "Send the completed grant applications to your state Action office prior to 01st March 1985. You may expect an answer to your application within 30 days."

When top agency officials learned of the letter last week, they sent a memo dated Jan. 18 to state and regional offices describing the letter as "outside regular channels," Malone said. It also reminded employes that "Action resources are awarded to qualified organizations solely on the basis of their merits" and that any inquiries about how to apply "are to be treated routinely . . . . "