The American Express card: Don't go broke without it.

Robert G. (Bobby) Baker sure didn't. Baker, a former whiz-kid Senate aide and Lyndon Johnson prote'ge' convicted in 1967 of larceny, fraud, income-tax evasion and conspiracy, filed for bankruptcy last week in Montgomery County. He claimed $384,955 in debts, including $72,000 owed to American Express.

That's right: $72,000 to American Express, the same people who never seem to let one nickel slide from month to month, the writers of all those letters designed to administer psychological kneecappings, and the employers of squadrons of telephone enforcers who come on like a combination of your ailing mother and a middle linebacker until they get their money.

"All of that $72,000 is pending since 1980, and it's from charges incurred in 1979 and 1980, according to the schedules filed by Baker," says bankruptcy attorney Brian Seeber, who has been appointed trustee of the proceedings. "Baker lists $72,000 approximately, and says that the claim is disputed."

Pending for two years! And approximately! After all those calls and letters, isn't the exact amount burned into Baker's pre-frontal cortex like a cattle brand?

"It's remarkable," says Seeber. "I don't recall a debt to American Express that high. Most people would have been sued long ago. But Baker states that he is not being sued by American Express. Someone had to take this out of the regular mill at American Express."

Informed that American Express refused to comment on this particular case, Seeber said: "I wouldn't talk about it either if somebody owed me 72 grand."

The average cardholder is curious, nonetheless. How did Baker, who gained ultimate notoriety as a convicted felon, talk them into letting him run the debt that high and long?

"There is no pre-set spending limit on the American Express card. The limit on charges is determined by income, ability to pay back and our previous experience with you," says one company spokesman.

But what if the eye of the average cardholder is caught by, say, a Rolls Royce Corniche, which is worth in the neighborhood of what Baker owes?

"You'd have a problem, there," says the spokesman.

Spokeswoman Nancy Muller explains that there may be no pre-set limit, but in fact there's "a formula" for determining what a cardholder, such as Bobby Baker, could charge. But the formula is "not anything that we make public. It's a very sophisticated authorization system."

And Baker is a very sophisticated guy.

"You're thinking that there's some special dispensation, but it's not true," says Muller. "As a rule, as a general rule, there are no special cases."

Then why hasn't American Express sued? Is it possible that in some cases, American Express doesn't do anything to collect?

"We don't not do anything," Muller is quick (and loud) to state. "There are 1,001 reasons why we might not have sued. Frequently we try many other ways. Usually you can say 'I can work something out with you. I'm expecting a check from my Aunt Tilly or my last employer.' People will say these kind of things and if we believe they're sincere, we can work something out."

Sincere is what Bobby Baker has always sounded, but how can American Express make sure that Aunt Tilly's check gets endorsed over to them?

"There are some sorts of means of getting it. I don't know what they are and I don't want to say."

But short of suing, it's all just words. How are you going to scare Bobby Baker, Lyndon Johnson's one-time golden boy, and doer of hard time, with a bunch of words? How can you scare anybody?

"There's a delinquency charge of 2 1/2 percent, or $10, whichever is larger," Muller warns, adding, in a tone of particular gravity: "After 30 days you can lose your card."

As it happens, Muller has just checked the computer for the word on one Robert G. Baker, but hasn't come up with anything. She will reveal that much about this sad case.

Is it possible that Baker owes nothing on his American Express card? That he filed this as part of his bankruptcy because he's playing for public sympathy, trying to turn himself into the Robin Hood of consumer credit? Or is he merely assuming that to be alive is to be in trouble with American Express?

In any case, imagine the television advertising possibilities: we see a shot of a guy with a vaguely familiar face standing in front of the Capitol, and saying: "You don't know me."

Neither, apparently, did American Express.