The chairman of the Federal Home Loan Bank Board, which regulates savings and loans, yesterday ordered an investigation into the way Shannon Ann Fairbanks, a top agency official, sought a $500,000 home loan using mailgrams signed with her title.

Chairman Edwin J. Gray asked the bank board's inspector general to be the fact-finder for the inquiry, but a determination of any wrongdoing will be made by the bank board's general counsel, whose office advised Fairbanks on how to avoid a conflict of interest when searching for a mortgage.

The general counsel's office reports to Fairbanks, who is the bank board's chief of staff, and to the three members of the bank board, according to an agency organizational chart that Fairbanks provided.

On Jan. 13, Fairbanks told her government secretary to send mailgrams to two dozen financial institutions in the Washington, D.C., area asking about the possibility of borrowing more than $500,000 for a home Fairbanks had bought in the "embassy area of the District."

The secretary ended the mailgrams with Fairbanks' name and bank board title. The mailgrams also included Fairbanks' telephone number at the bank board, where several of the mortgage lenders who received the correspondance called regarding a possible loan.

On Monday, Fairbanks sent handwritten letters to those who received the mailgrams saying that the mailgrams were personal and that her title was added to them inadvertently.

At Fairbanks' request, Gray yesterday sent a letter asking Inspector General Paul Gibbons to investigate "certain allegations" that Gray said were made in an article in yesterday's Washington Post detailing how Fairbanks sent the mailgrams.

The bank board's acting general counsel, Harry W. Quillian, will review the inspector general's report. He will decide if the facts show Fairbanks violated federal ethics codes and, if so, whether the violation was "trivial or significant." He said that part of his conclusion will hinge on whether the action in question was "deliberate or inadvertent" and on how much damage it caused.

The Inspector General's Office said that Quillian's conclusions are subject to review by the Office of Government Ethics, which is an independent unit within the Office of Personnel Management.

Gibbons said that among the things he will investigate is whether Fairbanks used a federal employe to do personal work on government time. Fairbanks has said the secretary used her lunchtime to send the mailgrams.

Gibbons said he also will gather facts on whether Fairbanks tried to influence the thrifts she helps to regulate. She has said she did not.

Before sending the mailgrams, Fairbanks said she consulted a lawyer in Quillian's office, who told her to document her search for a loan because of her position. The lawyer told her she could consider only bids available to others in the market.