NEW YORK (AP) _ Fare-discounting has gripped U.S. airlines fighting to capture more business, but the sales have confused the public and irked travel agents who claim they can't keep track of the fine-print restrictions.

''The sooner this is over, the better,'' Joel Wechsler, owner of Federal Travel Service in Boston, said Monday. ''I'd also look forward to some kind of rationalization of the airlines' pricing system, but that's probably too much to hope for.''

World Airways was the latest to offer a bargain, a $90 one-way fare between New York and San Francisco or Los Angeles, undercutting competitors by $9. The Oakland, Calif.-based carrier said Monday the sale is good through Feb. 15.

On Friday, Trans World Airlines entered the battle with 75 percent discounts, including $99 one-way coast-to-coast travel. TWA's ''New Getaway Fares'' apply to 400 U.S. markets, competing with bargains offered by American, United, People Express, Northwest and Continental valid until late March.

They generally require 14-day advance booking, purchase three days in advance, a 25 percent cancellation fee and a Saturday layover. Some fares are good for travel only on Tuesdays and Wednesdays.

A random sample of travel agents Monday reflected widespread exasperation with the fares because they were announced suddenly and have caused confusion among passengers unaware of the restrictions.

''We've had to reissue tickets, we've had to do more work,'' Wechsler said. ''In fact we may wind up with a net loss, because the lower the fare, the lower our earnings.''

Eric Munro, head of Travelwise International in San Diego and president of the local chapter of the American Society of Travel Agents, estimated that travel agencies can only make money on tickets costing more than $150.

''What frustrates me more than anything else is that people call you, then you spend an hour on the phone trying to explain to them what the restrictions are, and half the time the trips they want to take don't qualify,'' he said.

The holiday discounting and fare battles that have affected the industry over the past two months have overwhelmed many travel agents, who often read about them in newspapers before they are officially informed, Munro said.

''People will call and if you haven't read the paper that morning you're in trouble,'' he said. ''We have to call the airline and say, 'Hey, what is this, what did you come up with now?'''

Airline ticketing accounts for 70 percent of business for most of the nation's 26,000 travel agencies, according to the American Society of Travel Agents. The agency's commission generally is 10 percent of the net fare.

Some travel agents complained that airlines are advertising discounts but not alloting enough seats for them, which means the agents must call several carriers in attempts to book seats.

''The amount of work and the no-return is okay if the seats are there, if it doesn't take too much time,'' said Juergen Krenzien, head of Paul Klein Travel Service in Chicago. ''But when you have to research it, with 55 different rules and regulations, they make it so complicated.''

Others said they have received complaints from business travelers who find it difficult to take advantage of the the advance-booking and weekend stay requirements.

''They complain bitterly to me and sometimes to the airlines that it's not fair,'' said Wechsler. ''They feel that they're subsidizing the vacationer sitting next to them.''