"A bank is a place," wrote Robert Frost, "where they lend you an umbrella in fair weather and ask for it back when it begins to rain." But recently, after years of faithfully giving away calendars and toasters, bankers looked to have shed this image.

Then along comes a unanimous ruling from the California state supreme court that fees levied by that state's banks on customers who bounce checks are excessive and "unconscionable." That decision might not have been quite as serious if a bunch of House Democrats had not already been sponsoring tough legislation that would prohibit banks from denying their customers -- as some now do -- access to deposited checks for more than a week after the banks have collected the funds. For the bank -- which begins collecting interest on the deposit within 48 hours in practically all cases -- the present arrangement is profitable. For the ordinary bank customer who makes the mistake of writing a check some five days after a deposit only to have the check bounce for insufficient funds, the present arangement can be painfully expensive when he pays for the overdrafts and personally humiliating when he apologizes to creditors and friends.

Rep. Charles Schumer, a New York Democrat and one of the hawks in favor of mandating an abbreviation of what is politely called the banks' "delayed funds availability policy" and is popularly known as The Float, calculates just how profitable the present unregulated situation could be for banks. Taking the estimate of a company vice president that California's Bank of American earned $3.35 million a day from the float and suffered just $3 million a year in losses from bad checks, Schumer figures an annual profit of about $860 milion on the float for the Bank of America, a big bank but one that still represents only about 1 percent of the nation's banking industry. Schumer calls the banks' present apparent all-win, no-lose arrangement "a failure of market forces."

The fees that banks charge customers for checks that bounce, sometimes running up to $30 for one item, have not been justified by the Federal Reserve Board in congressional testimony. The average cost, "including losses," to a bank for a returned check, according to the Federal Reserve, is just 36 cents. And of the less than 1 percent of checks that do bounce, more than half are paid when presented for payment a second time.

A recent survey of 669 banks in 10 states conducted by the Public Interest Research Group found that seven out of 10 banks hold checks drawn on local banks for three days or more and three out of four banks hold out-of- state checks for more than a week. Consider that all this slow-motion inactivity is taking place at the same time the nation's banks are urging us to use automatic tellers, those miraculous inventions which, at 4 a.m. on a Thursday can, in the elapsed time of 13 microseconds, move enough money from your Christmas Club account in Cleveland to your checking account in Colorado Springs to pay your electric bill.

Any congressional action to mandate an abreviated period in which all banks give customers access to the funds they have deposited is opposed by the American Bankers Association. The ABA believes this "a matter for the bankers to address."

Fairness requires pointing out that the ABA's confidence in "voluntary" initiatives by the banks was at least partially vindicated by the same PIRG study that reported those lengthy delays to customers on access to their deposited funds. As of now, nearly one out of five banks commendably treats personal checks drawn on local banks the same way it treats cash, and one out of 10 banks even gives access, within just two days, to out-of-state personal checks. But such banks are still a small minority.

In many small banks in small towns, it is rare for checks to bounce because a deposit has not yet cleared. These are banks where the employees know the customer is "good" for the amount involved. Important customers, individuals of affluence and influence, are not bothered with bounced checks at banks of any size. Banks are frequently more considerate of those who are often golf or tennis partners of the banker.

But a lot of ordinary people who don't know their banker personally don't carry much clout where they have their checking accounts. The automatic tellers are making the whole relationship between individual and institution more impersonal. The banks' use of the float that delays access to funds is a real problem for people who live from paycheck to paycheck, who are concerned about making tuition payments and meeting car payments.

These are mostly people who need a checking account and credit to pay their rent and their phone bill, the kind of people who grew up in families that were Democratic when that party was the tribune of ordinary people, willing to stand up to the powerful forces and interests which collided with and often trifled with ordinary peoples' lives. For the Democrats, it's an issue that is relevant, practical and could be believable to a large majority of Americans, a rare Democratic experience of late and a terrific political opportunity. Let's see what they do with it.