The Civil Aeronautics Board unanimously gave formal but limited approval yesterday for airlines to meet and coordinate schedules at six major airports in hopes of relieving flight delays.

The meetings are to begin Wednesday at a Crystal City hotel where, according to a Federal Aviation Administration plan, the airlines are to discuss arrival and departure times at Atlanta's Hartsfield Airport, one of the six.

Discussions Thursday are to be devoted to Denver's Stapleton Airport and Friday to Chicago's O'Hare. Meetings next weekend would involve the three New York area airports, LaGuardia, Kennedy and Newark. Haste is necessary if airlines are to make adjustments in time for fall schedules, which take effect Oct. 28.

Although the FAA and its parent Transportation Department have vigorously sought the meetings to ease public pressure from passengers and other airport and air-traffic control system users, only the CAB can grant airlines immunity from possible antitrust actions if they meet to talk about schedules. In a purely economic sense, such meetings are regarded as anticompetitive.

Transportation Secretary Elizabeth Hanford Dole has threatened to impose a solution if the airlines cannot reach one, and the FAA has proposed a formal rule to do just that.

Dole called the CAB action "good news" and said, "I am confident the airlines can agree on revised schedules. If they are successful, there will be no need for government action to resolve peak-hour traffic problems."

The airlines, with a few exceptions, have expressed willingness to seek a voluntary solution. They are unified in their opposition to a government-imposed solution, calling the proposed FAA rule "onerous, unwarranted, discriminatory and economically damaging."

The CAB retained the right to approve schedule agreements and said the immunity would last only 45 days. Further, it said, the carriers could not discuss scheduled flights between specific cities and could not discuss "fares, rates, charges, capacity or in-flight services."

That would prevent, for instance, one airline from trading an early-morning Chicago flight to another for an early-morning Atlanta flight. The airlines will be able to discuss the New York area's three airports as a package, the CAB said, since to do so could "facilitate adjustments needed."