One might call him the Dear Abby of the pursestrings. Or the Sylvia Porter of the airwaves. Or perhaps the Sam Levenson for the money-minded.

Yet whatever Bruce Williams is called, he is called scores of times each weeknight by listeners from around the country seeking his help on matters ranging from retirement accounts to real estate, from credit cards to career changes.

Williams is the host of the first coast-to-coast radio network show on personal finance. He also is the National Broadcasting Co.'s candidate to take on the reigning monarch of the overnight babble beat, Larry King, whose program has been carried by the Mutual Broadcasting System since 1978.

The midnight mania has also struck the other networks. Last September RKO started a midnight to 6 a.m. call-in program out of Dallas and Los Angeles. The American Broacasting Co. inaugurates a similar show this April out of Los Angeles, and to the five hosts it has signed up it may add one specializing in financial affairs.

But for now, Larry King--who is heard by an estimated 3 million to 4 million insomniacs on 250 stations--is the man to beat. "We think we can beat him," said Maurice Tunick, Williams' producer. "We think Talknet the name of Williams' show is a better type of program."

Apart from late-night home audience participation, the King and Williams shows have little in common. King's is on for 5 1/2 hours and features guests; Williams' lasts two hours and features himself. King does theme shows on a wide range of subjects and then lets callers express their opinions on anything. Williams dislikes the term "theme show," but admits the subjects discussed usually have money as a common denominator.

King takes calls in staccato fashion from listeners phoning at their own expense. Williams sometimes spends 10 minutes with a single caller who dials in on a toll-free line. An annual $100,000-plus phone bill for Williams--and for Sally Jessy Raphael, whose advice to the lovelorn program airs after his as part of the Talknet package--is an indication of how seriously NBC is gambling that its personal-help format will be successful.

As for King, he says he doesn't regard Talknet as competition. "It's like a movie up against Johnny Carson," he says, arguing that the Talknet type of service show appeals to a different, older audience than his. Yet on a recent night, the average age of people calling Williams was just 37, compared with an average age of 32 for King's callers.

Talknet, which originates from the NBC studios in Rockefeller Center, made its debut last November. It is now heard on about 40 stations from Cape Cod to California. Washington, D.C., where it is heard live on WRC from 10 p.m. to midnight Monday through Friday, is its largest and most sophisticated market. One night last month, for example, a third of the callers were from the Washington area. In other cities, such as Baltimore, the taped show airs between 3 a.m. and 5 a.m., when King is on the air, and a few places carry it twice nightly.

In order to give listeners on the West Coast and in areas where the broadcast is delayed a chance to participate, NBC staffs the phones all night in New York, screens the callers, and then invites people to call back when Williams is there.

The calls are screened not only to weed out cranks, but to assure enough variety in the questions. Williams usually takes fewer than a dozen calls an hour, or about one in three who get through to NBC. The two lines available for New York state and the six for the rest of the country start to light up in the studio 30 minutes before airtime.

While the common denominator of Williams' show is money, Talknet is about as far removed from Wall Street Week as Lawrence Welk's orchestra is from the Boston Symphony. Williams purposely avoids discussing stocks and other investments except in the most general way. No one is allowed to mention company names (for fear of lawsuits). And the host punctuates his talk with endearments, cliches, homilies, and sometimes homespun tales about his family or about his term as mayor of a small New Jersey town.

His tone is mellow, outspoken, one of "global crackerbarrelism," in the words of Jerry Nachman, WRC vice president and general manager. Williams is occasionally glib and forcedly humble. "I'm no expert," Williams tells his listeners, and offers to put them on the air ahead of other callers if they catch him in a mistake. If he doesn't know the answer to a question, he may volunteer to have his researcher find it and call back.

"Where else can anyone with $300 get as much time as someone with $300,000?" Williams asked rhetorically in an interview. He claims to have had requests--which he says he has refused--from people with six-figure incomes to manage their money.

Yet it is the little guy who is the focus of the show. For every caller from Texas wanting to know if he should mortgage his house so he can live in Europe, there are more like the youth from Massachusetts asking how he could get his car payments rescheduled. Williams' answer: You're young enough to get a second job and pay off the remainder rather than getting a second, higher interest loan. To a bachelor in his 30s asking why he needed insurance coverage, Williams advised buying "insurance" now against the future possibility he could become disabled or the father of unexpected triplets.

He often calculates a contemplated real estate or business transaction and advises the listener whether it is feasible or wise. To do this, his producer says, "Bruce gets people to tell him financial things they wouldn't even tell their spouse. The listeners get a thrill eavesdropping on peoples' finances."

When he enters the broadcast booth, Williams arms himself with a legal pad, a mortgage rate book and a can of diet soda. No script. No economic tomes. Not even a calculator. How does he prepare for the show? "I don't prepare," he responds. Though he may contact his accountant from time to time, he says he does not regularly consult financial planners or brokers. "But I like to read--everything from Listerine labels to the Wall Street Journal."

He has no formal training in finance. Most of his business and financial acumen is derived from personal experience. At 49, Williams has been in broadcasting only six years and he regards himself primarily as an entrepreneur. At various times in his life he has run a private school, taught a real estate course, owned a wholesale florist business, run a car rental agency, sold insurance, started a bank, run a summer camp, peddled ice cream door-to-door and served as mayor of a small town.

He ran for state office as a Republican during the Watergate era. "I'm not even sure I voted for myself," he quips. "But if I hadn't lost, I would not have gotten into radio."

He began in New Brunswick in his home state of New Jersey. Later he moved his show to New York City, to which he commutes daily rather than abandon the country life. Two years ago he approached NBC. Last year the network finally gave him a two-year contract, renewable every six months.

NBC declines to reveal his salary. Williams says only, "I could live very nicely without broadcasting; it is not my main source of income." Industry sources guess NBC is paying Williams $50,000 to $75,000 a year.