In the bad old days the nation's governors would hold leisurely conventions filled with almost embarrassing pageantry, plenty of backslapping and sidelong glances at the big presidential sweepstakes.

The food, the booze, the limos, the elaborate entertainment all came courtesy of the corporate giants, and the governors paid little attention to federal policy, probably thinking it was mostly irrlevant to their needs.

As a result, Washington considered them irrelevant as an effective lobbying force.

While that may not have mattered in those old days, it matters now, because state economies are heavily affected by the billions of dollars they receive from Washington.

But the governors are now different too. At their just-concluded convention in Boston, they could not have been more spartan and serious-minded.

Gone were the freebies from the corporations; gone was the usual concluding "state dinner" with the drum rolls, the spotlights and the military escorts; and if not gone, the presidential politicking was far more subdued.

"It was almost as exciting as a convention of certified public accountants," said one observer of the National Governors' Association meeting.

In a sense the convention was a culmination of the governors' effort to change their image and rating with the White House and Congress. In the past few years, they have doubled the size of their professional staff (to 65), moved to a new building just 1,500 feet from the Capitol and tried to forge policies with the pros in government on important issues from welfare to urban aid to energy.

Today they will embark on a new test of their still-developing political muscle. Their leaders will see President Carter this morning and try to help him salvage his fast-shrinking natural gas pricing bill, which he considers a key part of his energy package, and which they consider crucial to the nation's economy ' and thus their own states' well-being.

"The president asked for an agressive energy approach that would be the moral equivalent of war," Michigan Gov. William G. Milliken said at the governor's recent meeting in Boston. Congress' response, he added, "has been the equivalent of sleep."

Whether the governors can help is not clear. First, the bill, which would deregulate the price of newly discovered natural gas by 1985, has lost support of powerful Senate liberals and conservatives. Second, the governors have had a mixed record this year in Washington.

They succeeded in persuading the president to include them in his urban policy. Carter proposed giving states $200 million a year for two years as incentives to do more for their fiscally distressed cities.

But almost immediately the governors undercut their position by sniping at the plan on Capitol Hill. They wanted more money and they wanted the White House, not the Department of Housing and Urban Affairs, to administer the program.

They finally came to terms with the White House by settling for the same amount of money but in different doses over the two years and a promise that a White House official would help HUD administer the plan.

But by then it was too late. Congressional sources said they were confused about what the governors really wanted, and committees of both houses - skeptical of the idea anyway - simply put it off until next year.

On another front, however, the governors had some success. Carter proposed eliminating states from his new $1 billion program of aid to local governments. Under a similar current program, states get one-third of the money.

Trying an end run, the governors persuaded Senate Finance Committee Chairman Russell B. Long (D-La.) to put the states back in the bill as it emerged from his committee. "We beat Carter on that one," said a triumphant state lobbyist.

They also beat Carter on another issue. He had proposed a bill that would bypass states in sending transportation planning money to cities, but through the efforts of Gov. George Busbee of Georgia, committees in both houses of Congress eliminated the bypass.

The governors are still battling a Carter measure that would guarantee anticrime funds to certain metropolitan areas. States allocate the funds and set the priorities. Since the measure is going nowhere this season, the governors are gearing up to fight again next year.

Several months ago they led an effort of state, county and local governments to fashion a cutback version of Carter's welfare bill. Ultimately, the measure failed for lack of time, but the administration has said it will become the basis of its effort to get a welfare bill next year.

Just as he headed their welfare and urban lobbying, Massachusetts Gov. Michael S. Dukakis is in the forefront of the governors' effort generally to become a powerful force in Washington.

It was the relentlessly serious Dukakis who set the tone for the Boston convention. Instead of the black-tie "state dinner," he held an informal clambake, and instead of limousines he provided buses to get there.

On the way to the clambake, he was telling how, in their post-Watergate purity, the governors had taken nothing from the corporations for their convention.

But as he entered a huge skating rink, where the clambake was in full swing, a reporter pointed out to him a huge banner across the arena. "United Technologies Welcomes You," it blared.

Dukasis winced. So did Stephen Farber, executive director of the governors' association. "I nearly dropped my drawers," Farber said later. It turned out that the conglomerate - which makes aircraft engines, helicopters, elevators and gas turbines among other things - was merely sponsoring a nonprofit country and western band.

But it smacked of the bad old days, when such signs filled their convention halls. Farber rushed across, the giant room, and instantly the banner came down.