During the first month of nationwide operation, interest-bearing checking accounts have proved more popular at savings and loan associations than originally anticipated, particularly in the Washington area.

According to several surveys released yesterday, 2 million new accounts totaling about $2.5 billion were opened during the first half of January. Among larger S&Ls, 83 percent offer these NOW (negotiable order of withdrawl) accounts, with another 9 percent planning to do so this spring. These figures were extrapolated from sample polls conducted by the Federal Home Loan Bank Board, the U.S. League of Savings Associations and the National Savings and Loan League.

It is estimated that between 50 percent and 60 percent of the $2.5 billion represents "new" money, i.e., funds that were not previously on deposit at the same institution. Much of that gain is believed to be at the expense of commercial banks from which customers have withdrawn their checking funds. However, U.S. League President Rolin D. Barnard noted with irony that the gain was not enough to offset withdrawls during the same period from passbook accounts.

His organization's survey of 1,431 S&Ls shows $2.3 billion in NOWs versus $2.5 billion in withdrawls during the first part of last month. (The bank board's estimate for NOWs is $2.6 billion during the first 20 days of January.) In New England it was ascertained that just 15 percent of NOW funds come from passbook savings. Industry sources admit much of the money from 5 1/2 percent accounts is going into money market mutual funds which now pay about 17 percent.

The National League, which sampled 300 members, put the average account balance at between $925 and $1,150. It found that 12 percent of S&Ls required no mimimum balance to avoid service charges, whereas 27 percent set the amount at $500 and 15 percent at $1,000. Those with minimal requirements opened 11 NOW accounts per $1 million in assets; those with the stiffest terms, 2 to less per million. The industry average is now 5 or 6. After nearly a decade of operation in New England, thrift institutions there average 30 NOWs per $1 million in assets.

A Washington Post Survey last December showed more than 95 percent of the metropolitan banks and thrift institutions polled intended to pay interest on checking. The minimum balance required to avoid service charges worked out on average to $355 for S&Ls. However, just 8 1/2 percent of them listed no service charge and no minimum-balance requirements.

This week The Post randomly polled a dozen local S&Ls on their NOW activity through the end of January. The average balance of actual accounts turned out to be $1,230, with a range from $625 to $2,500. In all cases the actual customer balance turned out to be higher than anticipated. The number of accounts established appears to be in inverse proportion to the average balance. Thus, three out of four of those with the highest balances had the smallest number of NOW accounts and vice versa. Not surprisingly, those S&Ls offering free checking with no minimum set up the most accounts.

One, which declined to be mentioned by name, set up 14,000 accounts totaling $11 million in the first month, 4,000 more than its goal for the entire first year.The average balance was $785. Next largest in number of accounts was Metropolitan Federal with 3,908, totaling $3.7 million. The average balance was $941. Neither institution imposes service charges or minimums. The danger, as experiences in New England, is that a lack of requirements will spawn many low-balance, unprofitable accounts. That does not appear to be the case here where both average balances are comfortably above the balance each S&L needs to break even on the account.

On the other hand, Perpetual American, the largest thrift intitution in the area, opened 2,988 accounts totaling $4.8 million, even though its minimum balance is set at $1,000, the highest for any thrift. The actual average balance of its NOW accounts is $1,600. Of all those surveyed, only National Permanent expressed any dissatisfaction with NOW activity. It has opened 1,500 accounts totaling $2 million and finds itself still far from its first-year goal of 5,000 to 6,000 accounts.

The percentage of new money averaged 63 percent, with associations ranging from 40 percent to 95 percent. County Federal attributed its 95 percent to having the third lowest minimum ($50) and initial deposit ($10) in the area.