Even as major league baseball continued to soft-pedal the idea of expansion today, members of the six-man Washington, D.C., contingent that presented its bid for a team Thursday say they like the vibes they are receiving.

"We've created a lot of our own steam with our breast-beating and whipping up the public in our own area," City Councilman Frank Smith, chairman of the D.C. Baseball Commission, said today, "but I think baseball took a major step in encouraging us by inviting all of us in. They were convincing to me that they were considering expansion as a serious possibility."

Commissioner Peter Ueberroth declined to be specific about the presentations by 12 cities over the past two days. Neither would Ueberroth be specific on whether expansion or relocation of struggling franchises will, in fact, happen.

"(Expansion and/or relocation) could happen as early as next year," Ueberroth said, "and may not come for several years."

He said the long-range planning committee will meet between now and baseball's annual winter meetings in San Diego, Dec. 9-13, to discuss both expansion and the possible relocation of struggling franchises. The committee then will make a report to all 26 owners in San Diego, he said.

"We've got a lot of material to digest," Ueberroth said. "One city appeared to have backed off from any interest and some cities we thought to be way down the line surprised us by showing their ability to be ready . . . much quicker than we thought." He wouldn't be more specific.

Ueberroth indicated that officials from cities seeking an expansion franchise were told that "pressure -- media or political -- would be counterproductive."

Asked if the letter President Reagan sent him Wednesday, offering his support for Washington, was "political pressure," Ueberroth smiled and said, "Next question."

The 12 members of the long-range planning committee again would not comment on individual presentations today.

Officials from Nashville, New Orleans, Buffalo, Phoenix, East Rutherford, N.J., and Tampa-St. Petersburg, Fla., made presentations today. One of the most interesting proposals came from the New Orleans group, which suggested that the Superdome might be used for the World Series if baseball opts for a neutral-site championship.

On Thursday, in addition to the presentation from Washington, officials from Denver, Vancouver, Indianapolis, Miami and Columbus, Ohio, made bids, with each group stressing points they felt made its city viable.

"We tried to impress upon them that our city has undergone a renaissance, a transconfiguration," said attorney Robert Washington, a member of the D.C. group that made a one-hour presentation. "I've been in enough business conversations to know when someone is not taking you seriously; when they shake their heads, say thank you, then show you to the door.

"That wasn't the case here. They asked us questions that went right to the heart of the issues."

Officials from several of the cities said the mere fact baseball held the sessions indicates a seriousness toward expansion. The consensus among these officials was that the screening process was not held just to appease the dozen cities.

Although it was difficult to get a fix on what the long-range planning committee members thought of the D.C. presentation, Robert Rich Jr., a leader of the Buffalo group, said that, in private conversations, he found the baseball executives to be "surprised and impressed" by Washington's presentation.

Although Ueberroth requested that officials of cities seeking a franchise not attend the San Diego meetings, Smith said the D.C. group may attend, anyway.

"We're reserving judgment on that right now," Smith said. "If it becomes real clear to us that (baseball) is aggressively pursuing this -- and we should be able to tell about that soon -- then we would honor the commissioner's wishes (and not go to San Diego).

"But if it becomes clear that something else would get ahead of expansion on the agenda and expansion would not be considered and that all we have been given is lip service, then we'll go back (to San Diego) and talk to individual owners and tell them why expansion belongs on the top of the agenda.

"I'm already convinced, though, that expansion is at the top of the agenda now."

An official from one city suggested today that since Washington's expansion drive seemingly has reached a crescendo, it might have difficulty sustaining its intensity should baseball decide to postpone a decision on expansion.

"You just can't turn people on and off," said Robert Pincus, president of D.C. National Bank and another member of the Washington group. "People in Washington can be cynical. To develop this momentum and then to pull the plug, it would be difficult to get it back again. We tried to emphasize that the time is right now."