The future of the Concorde is still in doubt, with environmentalists seeking to close U.S. airports to the supersonic jet while many others either praise the sleek craft or wish they could afford to fly in it. A 16-month test period of Concorde flights to Dulles ends next October. Meanwhile, no new Concordes will be built unless Britain and France receive further orders for the plane. Airlines are waiting to see if the lucrative Europe-New York route will be permitted.

By now, almost everyone knows at least two facts about the Concorde: It flies fast, and it makes a lot of noise. But, because of the prohibitive fares, few people have yet experienced the lavish treatment accorded Concorde passengers by the two European airlines who fly it, British Airways and Air France.

Since I nurtured a strong suspicion that Concorde service would make normal subsonic first class seem like the airborne equivalent of steerage, I looked forward to comparing the British and French concepts of the ultimate in airline luxury. I travel to Europe frequently on business, so to make my own Concorde comparison, I scheduled two flights: one from Paris to Washington on Air France, and the other - a few weeks later - from London to Washington on British Airways.

I purchased both Concorde tickets in London, as everyone who knows better should. This point is worth a digression because there's a bundle of money to be saved by following this advice. The precipitous decline in the value of the British pound has not yet been fully reflected in sterling-based airfares.

Thus, a one-way ticket from Washington to London, when purchased in the United States, is $801, and of course if you buy the round-trip ticket here you pay twice that amount, or $1,602. But if you purchase your ticket in London (or have it purchased for you and mailed to you), the Concorde fare between London and Washington (in either direction) will cost only 381 pounds - which, at the recent rate of approximately $1.65 to the pound, is $628, or a savings of $173. Similar savings are available at present on other flights to and from the British Isles (see travel section of Nov. 7, 1976).

If you plan to fly from Paris to Washington on the Concorde, it would be a lot cheaper to have the ticket purchased for you in London and mailed to Paris, and then use just the Paris-Washington coupon.

What follows is a journal of my two supersonic flights.

Paris-Washington via Air France

The check-in at Charles de Gaulle Airport is effortless, thanks to the special facilities set aside for Concorde passengers. My briefcase sports the elegant brown and beige leatherette tag that had been delivered with my ticket, along with a wallet of the same material.

At the departure satellite, I show my distinctive blue boarding pass and gain admittance to a special lounge where illuminated trees and lush plants create the aura of an elegant country garden. White-jacketed waiters scurry about offering champagne while a hostess provides a wide assortment of newspapers in several languages.

The first impression that registers once aboard the supersonic liner is the small size of the cabin, which brings back memories of the days of propeller aircraft. Seating is two-by-two on both sides of a narrow isle. I settle in by the window and find my seat to be the best designed airline seat I can remember, small, but comfortable.

Soon after takeoff, the cabin attendants begin their work. They are efficient and solicitous models of the genre. Cocktails are served - Chivas Regal, Beefeater gin, all premium stuff. To accompany the beverages, we are offered canapes of fresh Beluga caviar, cold lobster and delectable smoked salmon. More caviar canapes are passed about and, at these prices, no one is shy about taking seconds.

Soon the digital machmeter, which is on the forward partition, reads M105. We have broken the sound barrier with scarcely a shimmy.

The Air France dinner menu offers apologies to those who might have been expecting the classic French gastronomic feast by explaining that time and space don't permit. Instead, a meal characterized as a "Gourmet's Diversion" will be served. Based on the first course, no apology is necessary. The hors d'oeuvres are followed by a chateaubriand grille, small potatoes and sauteed cepe mushrooms. The wines are unusually fine: a Chateau Pichon Lalande 1970 red bordeaux, and a Moet et Chandon Cuvee Speciale. For dessert, we are offered a cholocate pastry or fruit, then coffee, assorted liquers and Havana cigars.

The meter reads M2.00, 1,350 miles per hour. I gaze out the peephole-sized window into darkness. The window is hot, the result of the tremendous friction on the aircraft's skin. From our 60,000-foot height, I can see light in the distance and the clean curvature of the earth. The sun had set on us hours earlier in Paris and we have caught up.

I check out the rear cabin and discover that the noise level in the tail end of the plane is considerably higher than up front. To my surprise, there are about 20 empty seats in the back. (As I later learned, the Concorde cannot fill all of its 100 seats and make it safely to Washington. At full load factor the aircraft would be too heavy for the fuel capacity, so at least 50 seats must remain empty on every westbound flight.)

Before landing at Dulles, a stewardess passes through the cabin offering a special deck of cards to each passenger, a souvenir of the flight on the world's first supersonic passenger jet. On arrival, solicitous Air France ground personnel expedite passengers with onward connections to their flights. Our luggage is waiting for us in the customs area. It is shortly after 7 p.m. in Washington. Four hours earlier, at 8 p.m. local time, we had been in Paris.

London-Washington via British Airways

At Heathrow's Terminal Three, a special Concorde check-in area assures passengers of no delays or waiting in line. A particularly welcome (although thoroughly undemocratic) touch is the special entrance to passport control reserved for Concorde passengers, eliminating a sometimes lengthy wait in a long time of cheerless adults and screaming children. At the gate, a special lounge offers amenities similar to those I found in Paris: newspapers, cocktails and hors d'oeuvres. An attendant takes passengers' coats and informs them that they need not worry about collecting them before boarding. The outer garments will be put directly on the plane.

When we board, I find the cabin interior of this Concorde similar to that of its French cousin, but something in the seat pocket catches my eye. It is a blue plastic case with "Concorde" emblazoned in gold in the lower right corner. Inside, I discover a wealth of goodies: earphones for the stereo music (there are no movies on Concorde), a boxed gold ballpoint pen, Concorde slippers, a Concorde eyeshield and a distinctive Concorde plastic luggage tag.

I also find an unusual mail-order catalog, written in English and Arabic, which offers assorted souvenirs like a garish gold and silver model galleon for a trifling $8,050 and a Piaget watch with two faces for only $4,800.

I take a quick look around the cabin and find the flight nearly full, save for the obligatory empty seats. The crowd is mostly male with a smattering of female passengers, mostly elderly and obviously wealthy.

Supersonic speed is quickly attained after takeoff. Cocktails and hors d'oeuvres match the standards to which we have become accustomed, in this case, smoked salmon and foie gras canapes to complement a cocktail service of premium liquors and champagne. An elegant menu with a blue cordon offers a choice of three entrees and makes no apologies whatever. On Air France there had been no choice.

The meal begins with caviar: This time, however, an individual tin is served to each passenger - no seconds. Wines are premium offerings as evidenced by the red bordeaux Chateau Brane Cantenac 1970 and, for champagne lovers, the especially delectable Don Perignon 1969.

I forego the duckling and the filet of sole and choose the sirloin steak. Suddenly, the aircraft veers to the left, nearly toppling the glasses of wine. The machmeter reads M2.00. The captain's grave voice now fills the cabin: Due to some minor technical problem, he has decided to turn back to London. We have been flying for an hour and a half, which means we must be halfway across the Atlantic Ocean. At this location, and traveling at twice the speed of sound, the last thing you want to hear about is "some minor technical problem."

The cabin attendants continue to serve lunch as if the captain's announcement had been made in Turkish and they didn't understand a workd. A rumor spreads throught the cabin - the problem is hydraulic. Hydraulic? Doesn't that have to do with the landing gear? Worried looks traverse the aisle while more drinks are ordered, with an implied sense of urgency.

At 4:15 p.m., the supersonic jetliner lands routinely at Heathrow Airport and we breathe a collective sigh of relief. Inside the lounge the bartenders are ready for us. While orders are taken and ice cubes clink into glasses, we are told that the back-up Concorde will be ready for a 7 p.m. departure. Loud groans fill the room and there is another run on the bar.

Five telephones are made in available to passengers and a hostess shows us how to dial the States. The temptation to make several transatlantic calls is overpowering.

We finally depart again, not at 7 p.m., but at 8:30. The captain apologizes for the delay, then jokes that we are indeed a unique group. After all, he chuckles, how many people can claim to have taken two Concorde flights in one day? We are not amused. At 7:30 p.m. local time, we land in Washington, over seven hours behind schedule.

How do British Airways and AIr France compare on their Concorde services? Well, for starters, I have to ignore the British flight's delay, which resulted in our arriving in the United States on a decidedly subsonic schedule. (With the characteristic British sense of fair play, the airline subsequently refunded the supersonic surcharge to the passengers on my flight.) It is only fair to point out that the sort of delay I encountered late last year has occurred only twice since Concorde service to this country began last May.

On the whole, both airlines go to extraordinary lengths to cater to their Concorde passengers. The extra service and amenities begin from the moment a ticket is purchased, and continue after the trip with the mailing of your supersonic certificate and a follow-up phone call from an airline representative to inquire about the flight.

Which airline is better? Comparisons at this level of service almost amount to hairspliting. I rate Air France slightly better on pre-flight amenities and in-cabin service, while British Airways offers a more varied menu and more interesting souvenirs.

In the end, what really comes through is that Concorde service is a throwback in time to the days when flying first class meant more than just a liberal company policy that allowed you to sit in the front of the plane. On Concorde, you get there in half the time, which is important enough - but paradoxically, the real key to Concorde's successful future may have as much to do with its level of passenger service. With the demise of transatlantic ocean travel, and the democratization of regular airline first class, the Concorde may well be the last refuge for those who demand the ultimate in personalized travel luxury.

An executive of a New York stock brokerage firm, Tanous is co-author of "The Petrodollar Takeover," a novel.