The tremendous traffic generated by the multitude of low air fares to Europe this year is resulting in more budget-conscious travelers than ever before using the Continent's rail systems.

"This rally to the rails is directly attributable to the bargain transatlantic air fares," a spokesman for Europe's railroads said, noting that today's economy-minded American traveler is intent on getting the longest possible run for his dwindling dollar.

Recently released figures seem to back up the railroad spokesman's observations. Americans are boarding European trains at record rates, and sales of [WORDS ILLEGIBLE] passes are steadily increasing as the season wears on. (Most Western European countries offer low-fare rail programs to vacationers.)

However, the big winner appears to be Eurailpass -- the all-encompassing pre-paid ticket available to travelers from North America that allows unlimited first-class travel for a set period of time on trains in 15 European countries. Sales of the tickets are up more than 20 percent over last year.

The tickets cost $189 for 15 days, $200 for 21 days, $270 for one month, $380 for two months, and $450 for three months of first-class rail travel. In addition, this year a Eurail Youthpass has been issued that is good for two months of second-class travel at $250 by anyone under 26 years of age. Both the Eurailpass and the Eurail Youthpass must be purchased before leaving the States.

According to Joseph Blumstein, chairman of the Eurailpass Executive Committee, the program is one of the biggest bargains in Europe today if you are going to do extensive traveling.

"To go by regular first-class rail from Paris to Vienna round-trip costs $207.80," says Blumstein, "while the 15-day Eurailpass costs $180 and that allows you to go not only between Paris and Vienna but just about any other spot in Western Europe for the same amount." He said the round-trip tourist-class air fare between the two cities is $350.

And with the price of gasoline at about $2 a U.S. gallon, there are no bargains in rental cars unless you can get two or three people to share the cost with you, he said. For a compact car and using the popular unlimited mileage weekly rate, Blumstein said, it would cost one person almost $500 to take a two-week round-trip from Paris to Vienna, allowing for taxes, insurance and fuel. "That's way more than double what a Eurailpass costs," he noted.

Besides the savings compared with other forms of travel on the Continent Blumstein notes, the rail pass has other bonuses even when the vacationer becomes "untracked." He said Eurailpass bonuses include free steamer and ferry passage and reduced bus fares.

Besides having unlimited access to the 15 rail systems, pass holders can ride free on the ferry connection between Brindisi, Italy, and Patras, Greece, via the Hellenic-Mediterranean or Adriatic Lines, which normally cost $45; save $26 on the Silja Line ship from Stockholm to Helsinki; save $16.30 on the Rhine River cruise from Cologne to Mainz, and take a free round-trip sightseeing excursion aboard a Swiss lake steamer from Geneva to Montreux, which costs $16.

The Brindisi-Patras trip and the Stockholm-Helsinki cruise are being offered for the first time this year, since Greece and Finland have joined the Eurailpass system. Other countries honoring Eurailpass are Austria, Belgium, Denmark, France, West Germany, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden and Switzerland.

You can get brochures, maps and other information on Eurailpass by writing to Trains, P.O. Box M, Staten Island, N.Y. 10305.