Two months ago, Peter Messitte was simply an uncommitted delegate to the Democratic National Convention from Montgomery County, a political specimen so rare and irrelevant that even state party officials refused to recognize his existence.

But this turbulent summer of politics has transformed Messitte, like many others, from factional oddball to potential power broker. With the help of a scrappy campaign of letters and phone calls and the prospect of a brokered convention, the 39-year-old Chevy Chase lawyer has become the organizer of a 100-member caucus of uncommitted delegates that will meet in New York Sunday with deputies of the party's two presidential candidates and the "open convention" leadership.

After that, Messitte says, it is anybody's guess what the uncommitted caucus might do.

"I don't think the group will be capable really of coming together on most of the issues," Messitte said in an interview yesterday. "But on procedural or rules issues, on matters where we have a common interest, we could work together.

"Every stripe of person is in this group," Messitte said, "pro-life, Kennedy people, from South Carolina, Indians from Nevada. Our numbers are not that impressive, but symbolically we're important. We represent a lot of people who have been disaffected with the candidates or didn't vote in the primaries."

Messitte's rise from Maryland's sole delegate elected as "uncommitted" to the organizer of such delegates around the country may have happened quickly, but it was not an easy change, he said.

In fact, when Messitte first wrote to state party officials to inquire about convention guest passes and other perquisites of delegates, he got back a letter advising him that if he wanted a guest pass, he should contact a delegate.

Messitte had to remind party leaders that he was, in fact, a delegate before his request were granted. "I realized that I was going to be an appendage to the Maryland delegation," he said. "It seemed that if I was going to have any voice in the convention -- not major, but audible -- I would have to get together with the other uncommitted delegates." a

Messitte wrote to Democratic National Committee Chairman John White to ask for a caucus room, telephones and floor passes for an uncommitted delegates caucus. The response, he says, was "a polite brush-off."

After waiting three weeks for a response from White, Messitte ended up meeting with an aide who told him that the Democratic National Committee "could not underwrite" the uncommitted delegates.

Next, messitte said, he talked to William Dixon, the convention manager, who "suggested that what we were doing was improper."

"He said we were a special interest group, like anti-nuclear or pro-life," Messitte said. "He said it would be a bad precedent for them to help us -- tht it might even violate federal election laws."

DNC spokesman Robert Neuman, maintained that Messitte was exaggerating.

"We told him if he wanted to have a caucus all he had to do was talk to the people in charge of reserving rooms, like all the other groups. He came to us wanting rooms and phones and floor passes and we couldn't give that to him because he's not a candidate -- uncommitted is just not an entity."

The Democratic National Committee never did offer to help him, Messitte claimed, but the Carter campaign volunteered to let the uncommitted delegates use the Maryland delegation's Carter caucus room Sunday night.

So far, Messitte expects Kennedy supporter Mark Siegel to speak to the group, and says White House political aides Richard Hutcheson and Anne Wexler and open convention movement chairman Edward Bennett Williams will show up or send surrogates.

"What's important to us," he said, "is simply to have a forum for all of the various factions. The presentations before Carter delegates or Kennedy delegates are clearly going to beslanted one way or another. If you go to the uncommitted caucus, in theory you should hear the most balanced arguments. We want to hear the positions of all sides and not the underbrush stuff."