Whatever it was Jimmy Carter had expected, it didn't turn out that way yesterday as the 155-member Democratic Platform Committee opened final hearings in Washington in preparation for the drafting of the party's 1980 campaign platform.

At a White House reception Carter gave the group last night he said he had received "good reports" about yesterday's session including, apparently, how well-behaved everyone had been.

"It was remarkably harmonious," the president said, starting to laugh, "almost as much as the campaign during the primaries."

Later, over wine and cheese in the State Dining Room, Carter and Kennedy supporters, who aren't supposed to be very friendly, not only were seen together but actually were speaking. Mostly, though, they were speaking to their own kind.

Hal Kwalwasser of California described the sessions earlier in the day from the vantage point of a Kennedy supporter as "real wired -- like, I mean, wired shut."

There's been a lot of talk about an "open process," Kwalwasser said, and yet when there were some disagreements over minor points yesterday, the Carter camp "made their people vote 100 percent down the line, a straight Carter position." Left on their own, Kwalwasser felt, "a lot of Carter delegates would not support the president on a lot of issues."

Thalia Schlesinger of Massachusetts (one guess whom she supports) a sister of Sen. Paul Tsongas of Massachusetts, said that even the two of them have disagreements.

"It doesn't mean that within that context we can't discuss them. But the June 3 primary," Schlesinger continued, "shows that a significant number of people agreed with Senator Kennedy, primarily on economic and foreign issues. So what's wrong with bringing that up before the convention?"

When Schlesinger spotted Hamilton Jordan, the president's new/old campaign cheif, she marched right up and told him that "the bottom line is November -- he better not get everybody so angry that they won't come back."

And what did Jordan say to all that?

"Well, the president didn't put him in that job for nothing," said Schlesinger. "Jordan's smart, real smart."

Testimony from members of Congress predominated at yesterday's hearing, and James Staples of Indiana said today's, focusing on special interests, are expected to range from gay rights to the MX missile, about 10 hours' worth, he figured.

"They told us when we came that we better have iron pants," Staples said.

R. P. Joe Smith of Oregon, who thought he sensed "a spirit of accommodation on both sides," said he was making his fifth trip to a committee hearing since they began in March, all at his own expense.

"Some state parties have funds for travel. Not Oregon, though. But if you're going to have an impact in politics," said Smith, "you have to be either rich, powerful or have knowledge. I decided I'd be knowledgeable."