The nomination of Edwin Gray, first vice president of San Diego Federal Savings, to the Federal Home Loan Bank Board has been put on hold while a political squabble is worked out.

The longtime associate of President Reagan would fill the board's vacant third seat and its chairmanship, succeeding Richard Pratt. Because there must be at least two members on the board, Pratt can't leave until Gray is sworn in. Pratt's departure date has not been announced, but his farewell parties have begun. Insiders say he will go before the end of April.

The Senate Banking Committee unanimously approved Gray's nomination last month and confirmation looked like a snap. But then the two Democratic senators from Arkansas, Dale Bumpers and David H. Pryor, asked the Senate leadership to keep the nomination off the Senate floor.

They acted because of a dispute over the Federal Home Loan Bank of Little Rock, one of 10 regional Federal Home Loan Banks. Three times in the past five years--including late last month--the Little Rock board has voted to move to Dallas.

Any move must be approved by headquarters in Washington, so the Arkansas delegation intervened once again with Pratt and the other board member, Jamie Jay Jackson, who is from Texas. The pair agreed not to discuss the move at last week's board meeting.

Spokesmen for Bumpers and Pryor deny there is any quid pro quo. Yet, they made it clear that the senators want to present Gray with their case against the move before allowing his confirmation to proceed. The Arkansas congressional delegation has held similar talks with all the other nominees to the board, and so far no FHLBB member has been willing to support the Little Rock board's request. SIPC SURPRISE? . . . . The Securities Investor Protection Corp., a quasi-governmental company funded by member assessments, is to stocks and bonds what the Federal Deposit Insurance Corp. is to bank accounts. Brokerage firms display the SIPC logo as a symbol of safety just the way depository institutions display the FDIC logo. As FDIC insures deposits up to $100,000 in the event of a bank's bankruptcy, SIPC insures investors against the failure of a brokerage firm. Accounts are insured up to $500,000, of which $100,000 can be in cash.

A few months ago, some customers of the Mount Pleasant Bank in Iowa had an unhappy surprise when the bank failed and they learned that the first $100,000 of their deposits were not covered by FDIC because they were in retail repurchase agreements--technically not deposits. Similarly, some 3,000 customers of the Bell & Beckwith brokerage firm in Toledo, which was just declared insolvent, may be in for a surprise because of another regulatory quirk.

SIPC covers cash balances only when the money is "resting" between securities trades. This is to prevent customers from violating New York Stock Exchange rules by using a securities account like a bank deposit account--earning interest but never buying securities or paying the firm commissions. (Dollars left in a broker's money market fund are covered by SIPC.)

The Bell & Beckwith customers kept their funds in interest-bearing "credit balance accounts," not money market mutual funds. But they also signed forms stating they would invest in securities at some time in the future. The accounts amount to several million dollars, sources say.

Of some 7,000 accounts, SIPC immediately declared about 4,000 eligible for insurance because there was sufficient evidence of trading. Michael Don, SIPC's assistant general counsel, wouldn't say how much activity showed up in the 3,000 other accounts. He said the statements of intent "may or may not be a factor" when SIPC decides if the balances are covered. The accounts, he added, will be reviewed on a "case-by-case basis." Don would not state the outcome of the handful of similar cases that have arisen in the past. --Nancy L. Ross