On April 23, many airline passengers will breathe a deep sigh of relief -- without inhaling cigarette smoke.

A federal law barring smoking on all scheduled flights of two hours or less will go into effect that day.

The law, part of the spending bill signed by President Reagan last week, is a compromise version of no-smoking bills that had passed the House and Senate earlier in the year.

In its final version, the smoking ban will last for two years and cover domestic and overseas flights scheduled to last two hours or less. That amounts to about 80 percent of all domestic commercial flights. Smoking cigars and pipes is already prohibited on airlines.

Under the new law, passengers who light up face up to $1,000 in civil penalties, and passengers who tamper with, disable or destroy smoke alarms in aircraft lavatories will be liable for up to $2,000 in penalties.

"If you scrounge around to save a few dollars on airfare and then pay a $1,000 fine, that's a pretty expensive cigarette," said Rep. Richard Durbin (D-Ill.), who sponsored the legislation in the House. Durbin said that he hoped to meet soon with officials at the Department of Transportation and the Federal Aviation Administration to discuss regulations to put the law into effect.

"This is a health measure, plain and simple," said Sen. Frank R. Lautenberg (D-N.J.), the principal sponsor of the bill in the Senate. "Airline passengers have the right not to have their health jeopardized by the smoke of others."

The congressional ban comes at a time of rising concerns about the impact of passive smoking. The state of California will prohibit smoking on regularly scheduled flights within California beginning Friday. Canada has a ban on smoking on airlines that took effect earlier this month.

Air Canada, which earlier this year began offering nonsmoking flights on routes from New York and Newark to Toronto and Montreal, gained customers as a result, said spokesman Stephen Pisni. With the beginning of nonsmoking flights on U.S. airlines, "we'll be back on equal footing, but in the meantime we will have gained all those people who will have discovered us" as a result of their preference for nonsmoking flights, he said.

Durbin said that flight crews would notify authorities at a flight's destination of violations and those authorities would enforce the law.

Confronted with the danger of smoking in the lavatories and the possible cost of lighting up in the cabin, most passengers will abide by the law, he said. "I don't believe this is going to be a major source of civil disobedience."