They do try to keep the mood light at the Federal Maritime Commission. By comparison with some other federal agencies, the atmosphere created by FMC Chairman Alan (Punch) Green Jr., an easygoing Oregonian, is somewhere between informal and funky.

The latest rib-tickler comes in an FMC announcement about a "program to discuss current issues in ocean liner shipping" to be held in Los Angeles on Monday. At the morning session, Green's counsel, Hugh N. (Rusty) Johnson, will talk about current shipping legislation. Green will speak at lunch. In between, the notice says, "attitude adjustment will begin at 11:30 a.m."

Judging from his confirmation hearing before the Senate Commerce Committee this month, the newest commissioner, Robert Setrakian, should fit right in with what he called the FMC's "collegial" atmosphere. Setrakian, a California wine grower and former executive of a defunct West Coast shipping line, told presiding Sen. Ted Stevens (R-Alaska) that the structure of the FMC, with its five presidentially appointed members, was conducive to "open and frank debate."

He had recently read, he remarked, that "making up your mind is like making a bed: it helps to have someone on the other side." The makeup of the FMC, he said, "supports that theory and serves that purpose."

Sens. Stevens and Daniel K. Inouye (D-Hawaii) had a little fun with a surprise gift for Setrakian. They presented him with a flag of the long-vanished Coastwise Steamship Line, of which Setrakian was president and a director in 1959-62.

Setrakian is expected to be confirmed by the Senate before the end of May. There is no word yet, FMC officials say, about whom President Reagan might select to fill the next vacancy on the FMC, which will occur at the end of June, when the five-year term of Commissioner Thomas F. Moakley expires. Moakley, a Massachusetts Democrat, reportedly is seeking reappointment, and his party affiliation actually gives him an advantage. Only three FMC members can be members of any one party, and there are already three Republican commissioners. * * *

AND GOOD RIDDANCE . . . It's a rare federal agency that is happy to announce a decline in its power and authority and a reduction in its staff, but the FMC put itself in that position last week.

The commission said presidential Executive Order 12418, signed by Reagan on May 5, would result in "increased operating efficiencies" in the government and provide "better service" to vessel operators.

The order transfers from the FMC to the Coast Guard--part of the Transportation Department--the job of enforcing rules that require ships sailing in U.S. waters to demonstrate their financial responsibility for oil spills. With the authority went 19 employes, transferred as a unit from FMC to the Coast Guard. * * *

FMC 11, ILA 7 . . . Despite vigorous pleas from the International Longshoremen's Association, which represents dock workers in East and Gulf Coast ports, the House Merchant Marine Subcommittee rejected, 11 to 7, a proposal to strip the FMC of its authority to inquire into the so-called 50-mile container rule. This rule, which is part of the ILA's master contract, is a job-saving device for ILA members, guaranteeing them work that would otherwise have gone elsewhere with the advent of containerized shipping. It says that containers packed within 50 miles of a port must be packed by ILA members, or else stripped and repacked by ILA members when they arrive at the docks.

The rule was recently upheld by the National Labor Relations Board, but it is still being challenged in proceedings before the FMC, which is responsible for regulating shipping rates.