A technologically advanced Web site for finding low domestic air fares--one that is easier, more powerful and better tuned to user needs than the fare tools used by Expedia, Travelocity, Preview Travel and other online travel leaders--is now available for use in a prerelease form. It's so much better than the others that it's worth adopting now for U.S. and Canada fare searches, even in this imperfect, limited version.

The unnamed air-fare search tool (located at www.itasoftware.com) was developed by former students in the Massachusetts Institute of Technology's renowned Artificial Intelligence Lab--the place where many of the exotic digital technologies that show up on the pages of Wired are born. I previewed the site, developed by the Cambridge, Mass.-based ITA Software, at its first public showing in November at PhoCusWright, an annual online travel meeting. Since then, the staff of The Washington Post Travel section and I have been testing the site, both to shop for our own travel and to perform research for stories, comparing results with those from established fare-search tools. When the site works (like any beta site, it's balked a bit), it consistently returns more lower-priced options, and better choices, than the leaders. On these pages we've often taken online travel agencies to task for claiming to deliver "lowest prices" and "ease of use" when in fact they deliver neither. ITA's software appears to be the first online fare tool capable of delivering.

A few caveats are in order. The site has a serious limitation--right now it works only when researching domestic and Canadian flights. (According to ITA Software President and CEO Jeremy Wertheimer, international flights will be added, in stages beginning with European flights, throughout next year.) And the site does not yet permit online booking of the air fares--you can print or copy down the information and take it to a travel agent, to the airline itself, to the airline's Web site or to another online travel agency to do the deed. And unlike online agencies, the site is now bare--no hot deals, no destination or lodging information, no package deals or cruises.

So what's the big deal? The ITA site's flight-search request--the form you fill out to tell the software what trip you'd like priced--corresponds masterfully with most shoppers' needs and desires. And once the request is tendered, the search engine returns the most thorough, flexible and usefully parsed array of fare and flight choices available on the Web. If the typical fare-search tool shines a narrow flashlight beam into a dark room to illuminate a specific group of fares, ITA turns on all the lights in the air-fare warehouse and lets you see pretty much all the lower-priced options in a single view.

For instance, ask the software to quote prices on a flight from Washington to Los Angeles. Before you start the search, it will let you open the query to any airports within a mileage range you choose (25, 50, 100 miles or more) or to any airports you specify (say, Dulles or National but not BWI, to LAX or Ontario but not John Wayne; be sure to separate airport codes with a semicolon, no space). You can also ask the tool to scan for flights within a time window ranging from two hours to two days, with different specs possible for departure and return.

All this is good but the best stuff is yet to come. When the site returns your answer, you see a screen highlighting the lowest prices that each carrier charges for that route during the time frame you've specified (thus answering the until-now-hard-to-answer "How much will it cost me to fly my frequent-flier carrier as opposed to the cheapest flight?"). It also lets you view price differences between flying direct and connecting once or twice. Click on "by airport," and the software slices the results so that you can see how much you save (or not) by using alternate airports. Is it worth it to fly from BWI with one connection instead of from National direct? What will it cost to fly to Seattle for vacation instead of San Francisco? Finally, you can make such calls with all the information you need--costs, times and routes. You can also parse flights by time, if schedule is important in your calculations.

Unlike most of the competition, ITA's engine lists flight options only after it has verified the availability of the number of seats you've requested. (The exception is flights on Southwest, whose prices ITA quotes even if they are not available. Southwest has contracts that limit its availability information to a tight list of partners.)

It keeps getting better. When you click on any fare for more information, you get airport-to-airport elapsed time (allowing you to add this to your value calculation), plus most caveats in plain English. If a connection you've chosen is very tight, the software inserts a red warning message in the margin. If a low fare routes you out of one airport and back via another, it red-flags that, too. It highlights some (but not all) of the conditions (such as nonrefundability) attached to highly restricted fares. It gives you all the booking information you need to consummate the transaction with the airline, a travel agent or another Web site. It even includes that elusive "fare code" information--so your agent won't be able to say he can't find the fare.

As anybody who has spent much time growing old and angry with the leading online travel sites knows, what I'm describing here is indeed worthy of the term "breakthrough," if not quite "godsend." It has the potential to be what the denizens of electroland call a "disruptive technology"--one so different and obviously superior that it threatens to realign an established marketplace in one swoop.

It is true, as the current online travel leaders will certainly insist, that not all customers come to the Web merely to find the cheapest air fares most easily. Some of them shop for specific times or carriers rather than low fares, some want one-stop shopping for air, lodging and cars, some want package deals and cruises, some want destination and planning information and some I suppose even want that "sense of community" and "interactivity" that e-commerce marketing people (and only e-commerce marketing people) croak about. But my guess is that the number of people who want the cheapest air fares most easily dwarfs the number of people looking for the other stuff--and that once this fare-search tool gets put in the marketplace by someone who adds booking, lodging and other features, it will quickly become the preferred site of savvy users. It will certainly obligate the others, principally Expedia and Travelocity, to continue their baby-step improvements to their older, more airline-centric fare-search technologies.

For now, the ITA fare searcher is a piece of technology in search of a commercial home--a company that can build an online travel business around this powerful, patented and potentially market-shaking piece of programming. I confess that I have fears that it will fall into the wrong hands, like the mythical 200 mpg carburetor allegedly invented by some engineer in the Midwest but purchased and then buried forever by terrified oil company executives. (Amadeus, a European company that operates one of the major clunky old central reservation systems long used by travel agents, is a 20 percent owner in ITA Software, but that arrangement doesn't preclude ITA doing deals with most other commercial partners.)

Wertheimer has been working on this project since 1992, when he was a grad student at MIT, and clearly takes satisfaction from having developed the software.

"It was fun," he says. "It was a hard problem, and we've solved it." He's been negotiating with various companies, including airlines, travel retailers and other groups, about forming a business relationship. He plans to add additional features and different kind of searches as the product comes to market. "Now the question is, what are we going to do with it?"

To Try ITA's Fare Tool

To use the "beta" (i.e., pre-release) form of ITA's flight-booking software, go to www.itasoftware.com. First click on the Our Technology button on the left, which provides a product overview. Then click on Try Our Beta Site; you'll need to register a logon name and password to use it. The site is simple to use (assuming you know the codes of the airports you want to check out; if not, go to http://www.flyaow.com/citycode .htm and bookmark the page). Use the Help function if you need to; the site, like many beta products, was balky last week, refusing to recognize some airport codes. Repeating the request seemed to fix the problem. Feel free to send feedback to ITA via the e-mail link (and copy it, if you like, to travel@washingtonpost .com). Unless you and your machine are really Java savvy, don't click on the "Use Java Client" box--it's for serious data-heads only.