Hi. I'm "Breathless" and I guess I'm going to let some airline fly me, but not until I get my strength back. I lost it on the phone. It seemed to me I had to.

I mean, in case you haven't noticed, "all airlines are alike" doesn't apply any more, and as the peas come out of the pod, they're beginning to differ sharply in terms of service as well as price. Some airlines also appear to be intent on imitating the savings-and-loan folks with bigger and better bonuses to customers.

Shouldn't a sensible traveler at least look into who's giving away the goodies, just how supercolossal they are, and exactly how the air hops differ? In theory, sure you should. In practice, I don't know. The problem is that you can't find out some of the most relevant things to know. At the same time, you won't win many new friends asking.

Since my little list of key questions was not so little, I calculate that I removed the possibility of a happy day from the lives of five travel agents and a score of airline reservations staffers.

But five airlines were going my way on a recent trip, and all for the same price. Furthermore, since they all have the habit of scheduling flights within 15 seconds of each other, I was pretty sure departure times would be "convenient." So I wanted to know exactly why I should take one carrier instead of another.

The Civil Aeronautics Board had intended to do a comparison study of airlines, covering such items as on-time performance, flight cancellation rates, baggage retrieval time, amount of seat space, cabin noise level, and the ratio of flight attendants to passengers. But don't wait up for that study. After three years of inaction, the CAB has just zapped the idea on the grounds that it would not promote competition or help the unaware consumer.

If you want to put such questions to airline reservations agents, you can, of course. I tried it and now have a large collection of hogwash answers. However, somewhere between what you might like to know and what you need to know is what you can know. Here, more or less, is where differences you can measure show up.

BASICS: It really is nice to know if the flight offered is "nonstop," "direct" or "connecting." Nonstop is the real thing: up, then down, with no landings in between. Direct means oops, the plane sits down one or more times. Connecting means lucky you, there's a change of planes involved before you get where you're going, and if you want to stretch the truth, you can add one more city to your list of "places I have visited."

If you ask, someone will tell you at which airport your flight leaves and departs. Ask. There are many variations these days. Laker's Skytrain, for instance, goes to Gatwick Airport (which I prefer to overcrowded Heathrow). But if you're only transiting London and plunging on elsewhere, Gatwick is not from where most flights leave.

The type of plane is something else you can ask about, because if you have a choice of carriers, wide-bodied planes like DC-10s, L-1011s and 747s are at least psychologically more comfortable than narrow-bodied ones such as DC-8s.

Friendliness is also a measurable thing. You must ask how easy it is to cancel a ticket and whether you can use that ticket with another airline at no extra charge. (The less you pay, the more restrictions.) And whereas most airlines are linked in joint fare arrangements, allowing you to buy one ticket to cover flights on several airlines and to have your bags transferred automatically, that's "most" but by no means "all." Foreign airlines in particular also differ in the extent to which their fares are "guaranteed" -- that is, not be raised before flight time.

Others vary in the degree to which they will provide for you in the event of delay or some other problem that's clearly their fault. People Express, one of the new low-fare airlines, for example, specifically exempts itself from looking after passengers in a situation involving delays.

A number of other big-name airlines also have rewritten their rules to allow themselves the option of providing free meals and lodging.

If you're a big-baggage carrier, be aware, too, that although the majority of airlines have the same rules, there are enough that differ to make asking a necessity. The free allowance can vary, as can the amount the airline will pay if it loses or damages your belongings. Commuter airlines can be different from major carriers, and flying in foreign parts can involve different rules from flying here. The rules for excess baggage in the Caribbean, for instance, are variable, and so is the cost of taking sports equipment in many places, as well as charges for oversized suitcases. One of the claims to fame of American, United and TWA is sizable carry-on baggage storage space, whereas some carriers make you check garment bags and anything else that's not "underseat" size. People Express goes even further: You pay for any baggage that won't fit under the seat.

Airline reservations agents should be able to inform you about these things, but don't bet your life on their doing it, even when they're asked. While some are exceptionally accommodating, it is not that unusual to find yourself suddenly disconnected if you seem to be taking too much time. If you book through a travel agent, though, and get your answers in memo form, you stand on excellent grounds in the event of a foul-up.

FROU-FROU. Coupons are out, rebates to frequent flyers are in, family fares may be making a comeback. That's the "gimmick" situation at the moment -- always subject to change, of course.

If you are digging for gold, though, don't stop there. As mentioned, you don't get very far asking, "Why should I fly your airline?" But you can profit by asking, "Do you serve food?", "Any choices?", "Is there a movie?" or "Any special hotel or car-rental discount deals?"

Cross your fingers and hope you get correct answers, because the boys in various airline backrooms have come up with lots of what they hope will be interesting extras, even if they're not always communicated to the sales people.

For instance, Midway Airline sells "executive ticket books" containing 10 tickets with any combination of cities and/or fares, the advantage being that the fare is then not subject to increases for one year. Western has a travel-pass scheme that provides $10-a-flight credits; once you've clocked five or more flights, you get $50 off a more expensive flight; 50 flights gets you $500 off. Western has "Sip Slips," seven drinks for $10, on sale at ticket offices or airport counters, and an "Instant First Class" plan that allows any full-fare coach passenger to upgrade just before departure for an extra $20.

Pan Am has a 10 percent to 20 percent hotel discount scheme for New York City, called "New York Travel Break." Continental has a valuable freebie in its "International and Domestic Travel Guide," which gives useful arrival and departure information, how to get to town for how much, and so on. Continental also has a $16-a-day car-rental deal with Dollar. Laker, Pan Am and British Air are among those offering discount hotel arrangements for passengers to London.

American has just introduced the "AAdvantage" which rewards passengers who fly 12,000 miles or more each year with a variety of freebies. This has now been matched with comparable programs by TWA and United. (Rebates, of course, are illegal, so these are called incentives and other names. But with deregulation, direct kickbacks by travel agents to commercial customers are reportedly a big item in some parts of the country. Incidentally, while airlines mail you your ticket, a travel agent may be agreeable to delivering it.)

But understand that the airlines are playing hardball. Most will no longer tell you anything at all about their competitors' schedules, prices or destinations, or whether their own fare is the lowest in the market. Once upon a time they did.

Nor do they have any legal obligation to write a ticket that uses all the fare "loopholes." A business traveler who recently bought a coast-to-coast ticket with stops in two cities in between learned that the hard way. He paid almost $1,100 for what could have been a $600 trip.