The Senate authorized $15.6 billion for the nation's airports and air traffic control system yesterday, aiming the measure at congestion in the skies that is expected to worsen.

The legislation would guide federal spending during the next three years to improve airports and modernize aircraft-tracking equipment. It also would help pay the government's 15,400 air traffic controllers, 1,900 aircraft inspectors and other workers.

"There's a lot of frustration with what's going on in relation to lateness of flights and luggage not arriving on time," said Sen. Wendell H. Ford (D-Ky.), chairman of the Senate aviation subcommittee. "But the important thing is {that} you as a flying passenger arrive at your destination safely."

The Senate approved the measure, 96 to 1.

The nation's airlines carried 278 million passengers in 1978, which is when the government stopped regulating airline service, including rates and routes.

The number of passengers has increased to an estimated 450 million this year, and the Federal Aviation Administration projects it to increase by 4.5 percent annually to reach 700 million by 1998.

In addition, the number of takeoffs and landings is expected to grow from 61 million this year to 79 million in 1998.

Passenger frustration also has increased: The Department of Transportation reported 5,611 complaints from consumers in September, down from 7,280 in August, but up from 1,088 in September 1986.

Lawmakers, airline officials and others have argued that one of the best ways to make flying more pleasant -- and safe -- is to modernize the system.

They argue that the air traffic system needs modern computers, and note that the last major airport constructed in the United States -- Dallas-Fort Worth International -- was opened in 1974.

To that end, the bill would authorize the government to spend $4.9 billion for the 1988 fiscal year, which began Oct. 1, $5.1 billion for next year and $5.6 billion for fiscal 1990. The money would need to be provided in later legislation.

The measure directs that about $1.7 billion be spent annually to expand and modernize airports, up from $1 billion this year.

In addition, $1.5 billion would be spent each year to modernize air traffic control equipment, about double the current amount; $1.7 billion would pay salaries; and $200 million would be for research programs.

The money would come from a special fund the government maintains for aviation programs. Revenue from taxes on airline tickets, air freight and aircraft fuel is placed in the fund's coffers.

The fund has a $5.6 billion surplus, which upsets some lawmakers and airline officials who say the money should be spent faster.

The lawmakers agreed to an amendment that would extend a program for 10 more years in which the government subsidizes air carriers that serve about 130 small communities. The provision, sponsored by Sen. J. James Exon (D-Neb.) also would allow new towns to join the program if they agree to pay half the subsidy. The program, which costs $24 million annually, is due to expire next October.

On final passage, Sen. William Proxmire (D-Wis.) voted against the measure. Sens. Albert Gore Jr. (D-Tenn.), Terry Sanford (D-N.C.) and Minority Leader Robert J. Dole (R-Kan.) did not vote.

The House approved a five-year, $28.5 billion version of the bill on Oct. 1. The two houses will have to agree to compromise legislation before it is sent to the White House for the president's approval.