Two leading congressional proponents of reduced federal aviation regulation joined forces yesterday to support legislation that would give airlines more freedom to begin new routes and to increase or reduce fares without prior Civil Aeronautics Board approval.

Sen. Edward M. Kennedy (D-Mass.) and Howard W. Cannon (D-Nev.) introduced the Air Transportation Act of 1977 and called on their colleagues and President Carter to make passage of CAB reform "the number one item on the regulatory agenda."

Cannon said he would begin hearings on the bill March 21, before the Senate Commerce Aviation Subcommittee that he heads.

In a separate development, congressional staff sources said Florida Democrats have urged Carter to appoint Sylvan Meyer, former editor of the Miami News, as CAB chairman. Both of the state's senators, Democrats Lawton Chiles and Richard Stone, have urged Carter to name Meyer, currently president and publisher of Miami Magazine and a licensed pilot.

Florida's Democratic organization has selected a CAB post as their top priority request to Carter, whose plurality in the Florida primary last year was a significant boost in an ultimately successful drive for the Democratic nomination. State party chariman Alfredo Duran reportedly met with Carter last weekend to discuss the CAB chairmanship.

The decision of Kennedy and Cannon to join forces on the subject of reduced airline regulation was viewed as enchancing prospects that the Senate will pass such legislation this year. Hearings on similar proposals are planned in the House.

While the Carter administration has not taken a firm stand on airline reform, Secretary of Transportation Brock Adams repeatedly has expressed his opposition to complete "deregulations."

In his first major speech here yesterday, Adams told the Consumer Federation's Assembly that the administrations plans to work with Congress "to develop reforms which will make the system of air regulation work better and my primary concern is for protection of the consuming public."

Adams noted that he recently authorized his department to support proposals for greater service at lower fares in an out of Midway airport in Chicago. "We will be watching this case carefully to see whether the regulatory system is functioning well," Adams stated.

The most significant compromise between previous proposals of Kennedy and Cannon, in the legislation offered yesterday, involves freedom on entry into the airline business.

Kennedy had called for permitting airlines to offer any new services, after an initial four-year period. Cannon had opposed this open entry and called instead for some changes in CAB policies.

Under the legislation introduced yesterday, the five largest domestic lines - United American, Eastern, Delta and Trans World - would be permitted to add one new market each year, starting Jan. 1 on the second year after enactment. The new routes would have to be under 2,000 miles each.

All other domestic airlines intrastate carriers and charter airlines would be permitted to add up to four new markets a year, starting Jan. 1 of the first year after enactment and limited to 4,000 miles a year.

Kennedy and Cannon proposed that airlines could raise fares as much as 10 per cent through Dec. 31, 1979, and 20 per cent thereafter without prior CAB action. In addition, under the proposal, fares could be cut as much as the airlines want so long as direct costs are covered.