Atlanta ? Delta Air Lines’ plan to cut its most expensive fares and ax a Saturday-night stay-over rule for cheaper tickets could be a boon to business travelers. But some rivals balked at the idea and analysts warned the move could reduce the already struggling industry’s revenues as much as $3 billion a year if every carrier followed suit.

Shares of airline stocks slumped after Wednesday’s announcement.

Several other airlines were reviewing Delta’s plan. None immediately matched it nationwide. And two discount carriers, Southwest and AirTran, said they already offered lower fares than Delta’s new model.

One thing is for sure from Delta’s decision, analysts said: The days of paying top dollar for domestic flights are numbered as major airlines try to win back business travelers from discount carriers and fight off mounting losses.

“They need briefcases on airlines to make a profit,” said Terry Trippler, an industry expert in Minneapolis who runs an airline information Web site.

On Wednesday, Delta Air Lines Inc., the nation’s third-biggest carrier, announced that it was cutting its most expensive fares by as much as 50 percent nationwide and was eliminating other restrictions in an effort to woo business travelers and last-minute buyers.

Delta said no fare would be higher than $499 one-way in coach class or $599 one-way in first class under its new program, which it advertised in newspaper ads in several of its key markets.

Analysts and airline officials stressed that not every ticket buyer would see a fare reduction. Leisure travelers were not likely to benefit, because they generally buy their tickets well in advance of their trips. But this would make Delta’s fare structure easier to navigate. Airline executives also said that in the short term, the program could lead to lower revenues for the struggling carrier, but it could benefit Delta long-term by bringing in more customers.

“We expect a significantly hostile industry response,” said Jamie Baker, J.P. Morgan airline analyst.

Delta Air Lines Inc. is cutting its most expensive fares by as much as 50 percent nationwide and is eliminating other restrictions in an effort to woo business travelers and other last-minute ticket buyers. But other carriers are reluctant to match Delta's move.

Merrill Lynch analysts cautioned that if there was an industrywide adoption of Delta’s overhauled fare structure, the nation’s carriers could see their combined revenue reduced between $2 billion and $3 billion annually.

Delta’s shares sank 51 cents, or nearly 7 percent, to close at $6.80 on the New York Stock Exchange. Northwest shares fell $1.04, or 10.8 percent, to close at $8.60 on the Nasdaq Stock Market. Continental shares fell 99 cents, or 8.1 percent, to $11.21 on the NYSE, where American was off 96 cents, or 9.6 percent, to close at $9.05.

The nationwide program went into effect Wednesday. Those people who bought full-fare tickets before Wednesday can exchange them for the reduced fares if they pay a $50 fee, spokeswoman Benet Wilson said.