There you are -- ready to slip into two weeks of vacation at last.

Sorry, they nicely inform you, they've overbooked your flight. They've bumped you until tomorrow. Or they've lost your bags. It's a traveler's nightmare.

It's also an example of some of the flight service areas in which airline passengers can expect major changes by December or earlier. That's when decisions are due on pending regulations by the Civil Aeronautics Board, the federal agency which oversees all airline operations.

In 1978, Congress established a schedule for the gradual elimination of CAB jurisdiction over routes, fares, mergers and other aspects of airline travel. The differences anticipated for this year come as part of the setting of the CAB sun, whose slow but sure eclipse is set for Jan. 1, 1985. By the December 1982 deadline, rulings concerning baggage, overbooking, grievances and amenities will be made and will remain in effect until Congress either transfers or abolishes the authority of the CAB at its dissolution.

Meanwhile, the CAB is still packing its baggage ruling into shape, not yet sure what to take and what to leave out. Three basic options are being considered.

One is a retention of all conditions currently in effect, which means for delayed, lost or damaged bags on a domestic flight each airline would follow its current $750 ceiling per-person liability. No other rules would be set for bags.

A second choice includes retaining all conditions currently in effect, but incorporating in a code all rules about baggage determined by the CAB. For example, in addition to the $750 liability ruling, the CAB would set forth regulations on fragile or perishable items, on excess value coverage to increase the airline's liability. Also, the CAB would include a ruling allowing passengers 45 days to make claims.

The third option open to the CAB is to eliminate all government regulations, allowing the airlines to set their own individual policies. And although it may sound as though air passengers could be left holding no bags, it is likely that most airlines will continue to ensure proper baggage care.

"If we damage a bag, we'll take care of it, because we do have a responsibility," said Charles Novak, manager of corporate communications for United Airlines. "Just like a warranty on a dishwasher or automobile--they'll fix it for a year--United Airlines will fix something that goes wrong."

The Aviation Consumer Action Project, however, is not so assured of proper repairs. "We think you're better off with the regulations now," said Matthew H. Finucane, director of the ACAP. He predicts problems for consumers if airlines are left to deregulation and he is arguing for a $1,000 liability to counteract the possibility of a lower liability rate. His group also is afraid that if airlines make the rules while trying to survive in a competitive market, policies could be set to exclude some items--such as cameras, for example--from liability coverage.

Another area up for new regulation by the end of this year is overbooking, or oversales (meaning a passenger holding a reservation may be denied a seat).

During the PATCO strike last August, there was a surge in overbooking, leaving 17,067 people involuntarily bumped from flights during that month. Another 16,157 passengers were bumped voluntarily from overbooked flights. As of November those figures had dropped by about 7,000 in each category, but the problem still is a common one.

Currently, passengers voluntarily bumped are paid a premium offered or negotiated by the airline. Carriers are required by the CAB to pay anyone involuntarily bumped the fare to his destination ($37.50 minimum, $200 maximum), plus the passenger gets to keep his original ticket, which he can use or return for a refund. Proposals affecting this ruling would include:

* Dropping the $37.50 minimum payment because many short fares are less than that;

* Dropping the compensation if the passenger makes it to his destination within an hour of the involuntary bumping;

* Changing the compensation to apply only to an overbooked part of a multi-leg flight.

Two other rulings are being considered in connection with oversales. One would be a relaxation of rules governing overbooking on U.S. inbound flights from overseas, allowing the U.S. airlines to better compete with foreign airlines; the other would be the elimination of all rulings, leaving the airlines to set their own policies.

Another area which will undergo a change this summer is in the gripe department. The first step in any grievance procedure is to go directly to the airline. The next step available is the Civil Aeronautics Board complaint offices. However, as of this August, offices in New York, Chicago and Los Angeles will be closed as part of the deregulation plan. The Washington office will be the last to shut its doors.

As part of the preparation for closing, however, the CAB reports that it has been successful in starting programs in state and local consumer agencies to handle complaints. Most airlines plan to continue their consumer affairs offices for dealing with problems. As a final recourse, grievances can be taken to small claims court.

Amenities and Information are the two areas which will be affected indirectly by the CAB rulings this year.

Under the category of Information, the Board has ruled that it will require airlines to provide passengers with certain facts. The ruling, for which the public comment period is already closed, will lie dormant until the baggage and oversales situations have been decided.

Under the category of Amenities, airline passengers may or may not see a tightening, depending on the financial state of the airline or the priority it places on providing amenities.

For many years the CAB required airlines to file their amenities policies. Now, however, the Board has allowed airlines to change their rules, and for some airlines the customary complimentary meals, accommoda- tions, ground transportation and long-distance phone calls for passengers delayed by natural causes (such as inclement weather) have been eliminated. It is a good idea to check with the airline before traveling to be aware of what is offered.

The goal of government, as consumers watch the authority slowly being stripped from the CAB, is to allow each airline to adopt more reponsibility and ultimately to set rules guided by its own competitive market environment. With regulations dictating, the government feels that some element of competition has been lost. As the CAB is phased out, it is hoped a healthy marketplace will govern to the advantage of both consumer and airline.

"There will be a lot more opportunity for carriers to do things, to experiment," said a Pan Am spokesman. "At times the airlines will be able to match their competitors and at other times they won't. It'll be like any other free-enterprise situation."

Despite the turbulence expected by the end of this year, there still is time for the prudent air passenger to prepare himself with knowledge of the rules of the flying game.

According to CAB spokesperson Desta McDowell, "Fly-Rights," a free 28-page booklet on rights of airline passengers, will be issued free by the CAB as long as supplies last. After that the booklet will available for a slight fee through the Government Printing Office. It is a comprehensive guide for any air passenger and includes rules on all aspects of flying, including insurance, safety and reservations rights. To obtain a copy write to: Publication Services, Civil Aeronautics Board, Washington D.C., 20428.

Although the public comment period for oversales has closed, the CAB invites proposals on baggage rules. Written proposals must be postmarked by April 5 and should be submitted to the Civil Aeronautics Board in Washington, Docket Section, Docket 40366.