The nation's airline passengers, already hit with reduced flights and delays as a result of the air traffic controllers strike, soon may be faced with higher fares as airlines phase out or restrict the use of discount tickets.

One of the chief goals of the new fare structure appears to be to prevent the use of discount fares for business trips.

United Airlines, an industry leader, has announced that it will raise its discount fares on many transcontinental flights by as much as 51 percent. At the same time, it said it will reduce regular fares by about 45 percent on those same routes beginning Oct. 1.

Wall Street analysts yesterday said the expect other airlines to follow suit. Since the strike began Aug. 3, the airlines have been forced to reduce the number of flights and subsequently the number of seats available. Because fewer seats per flight now will be empty, the airlines say discount fares won't be necessary to lure hesitant passengers.

Most of the cuts in discount benefits will occur this fall after the Federal Aviation Administration announces its new airline flight reductions resulting from the strike, said Eliot Fried Jr., and industry analyst for Shearson Loeb Rhodes.

"It doesn't mean discount fares will be eliminated," Fried said. But he said industry executives have told him that they are incluned to require that ticket purchases be made 14 days in advance of departure. Some discount flights currently require that purchases be mae seven days in advance, while others have no advance purchase requirement at all. Fried said many airlines also will require passengers to stay at their destinations over part of a weekend to prevent some, "if not all, business travelers" from using cut-rate fares.

"You're going to see less discount fares, that's obvious, because you're going to have more seats to sell," said Bill Berry, spokesman for Delta Air Lines, which philosophically has opposed many discount fares as "giveaways." Discount fares "should sell a seat that otherwise would not be sold," he said. But pressures to cut flights will allow airlines, already losing millions of dollars daily because of the strike, "to raise [price] levels on normal fares," Berry said.

Delta, one of the nation's most profitable airlines, has no immediate plans to raise its discount rates, Berry said, but he added, "You may find in the future we'll allow these [discounts] to expire."

The average super saver discount of 35 percent probably will drop to about 20 percent, said Alfred Norlinger, an airliner industry analyst for Kidder, Peabody.

ybut Hans Pickert, an analyst for E. F. Hutton, said that without the strike, the financially pinched airlines probably would have eliminated some super saver fares and tightened restrictions on others anyway.

Requirements on the super savers, which were started four years ago to fill flights, had become so loose that business people were using them, Pickert said. For example, Northwest Airlines already had proposed an overall net increase in discount fares effective Sept. 16, said Peter Houghton, Northwest's director of tariffs.

The routes most likely to be affected by changes in discount fares are vacation routes, Fried said. "I think everybody's going to change their fares, but they're not going to say it."

Many of the major airlines said they wre studying whether to follow United's lead in reducing discounts on coast-to coast flights. "We want to see what the strike is doing to discount fares," Houghton said.

"We'll see some juggling in the next few weeks," said David Venz, a spokesman for Trans World Airlines. "It's likely the other carriers will do the same" -- match United or offer a different kind of fare structure.

United said it lowered its normal first-class and coach fares for coast-to-coast flights to reduce the price difference between discount and full-price tickets, a difference which "encourages, if not forces, travelers to use discount fares."

United's current coast-to-coast discount fare will rise from $298 to $450 by Oct. 1. Its first-class round-trip fare will be reduced 45 percent from $1,340 to $750. The round-trip regular coach fare will drop from $965 to $600. The fares will apply on trips between New York, Newark, Philadelphia and Allentown, Pa., and 10 cities in California, including Los Angeles and San Francisco. United's fares between Washington and California will remain the same.