To make one thing perfectly clear at the outset, everything you've heard about the D.C. Republican Party is probably true: its members can meet in a telephone booth, they can drive to their national convention in a VW and it's easier to find a parking place in Georgetown than a card-carrying Republican in Anacostia.

But this year, as the city's GOP delegates prepare for the national Republican convention in Detroit, the city's 14-member delegation is feeling more isolated than ever.

In Detroit, it will be the only delegation that is 100 percent for George Bush at a convention that is largely a coronation for Bush's victorious rival, former California Gov. Ronald Reagan.

Also, the D.C. delegation -- half black and all urban -- represents a moderate-liberal element in the party at a time when the GOP's conservative forces appear to be asserting control of the party for the first time since 1964.

And when the District delegation returns home, it will find its own efforts to broaden the local party's racial and economic base set back, perhaps permanently, because of a power coup by conservative Reganites from the affluent precincts west of Rock Creek Park.

The District's minuscule Republican Party -- only 8.9 percent of the city's 253,000 registered voters -- had traditionally been a clubby, predominantly white organization from the city's Ward 3 west of the park. In the last few years, however, it had begun to broaden its base to include more blacks, more young professionals and members from the city's other seven wards.

But last Feruarry, a Ward 3 group formed its own "Committee to Rebuild the Republican Party" to challenge the broader-based party leadership in the May 6 primary elections. It won 63 of the 70 seats on the D.C. Republican Committee.

The power struggle in the D.C. Republican party perhaps mirrors the current tug-of-war in the national party between the conservatives that comprise the core of Reagan's supporters, and the moderates, who have been trying to broaden the party's base to include minorities and urbanites.

"It's a power struggle for the party's base," said Cecil Grant, Bush delegate and one of the few Republican moderates who survived the election coup.

"We were at the threshold of getting some new, young blood ready to roll," said Arthur Fletcher, chairman of the D.C. delegation and the party's 1978 mayoral candidate.

He said that the Rebuild committee of Ward 3 Republicans felt that the Bush delegate slate offered by the party leadership was too weighted to the other wards of the city. They were espcially incensed, said Fletcher, since Ward 3 supplies the bulk of the money for the local GOP.

"They felt that not enough people from the third ward -- where most Republicans live -- were included on that slate," Fletcher said. "If you continue to concentrate all of the participation in one ward of the city, then the chances of broadening the party are rather remote."

On the other side, the Rebuild committee Republicans said their power coup was brought about partly because the old party leadership -- like Fletcher -- was trying to keep the Wrd 3 Republicans out of any position of power in the local party. One Rebuild Republican said, "Now is the time to find out where the power is in this city."

Added another Rebuild committee member, "If the majority of Republicans live in Ward 3, then why shouldn't a majority of the state committee be from Ward 3."

The ousted leadership, says Michael Gill, the District's GOP national committeeman and a Reagan supporter, was making the party too liberal, so that it was out of the mainstream of traditional Republicanism. For instance, Gill said the old leadership was pushing for all congressional voting representation for the District -- which would inevitably lead to two more Democratic senators and at least one more Democratic congressman on Capitol Hill.

What pushed Gill and some others to defect and form the new Rebuild committee, he said, was the central leadership drive to field a full Bush slate, instead of a compromise slate.

"The small group of people who were for Bush -- and were predominantly black -- saw after [the] Iowa [caucuses] that they could take control of the party," Gill said. "So 21 of us defected and formed a full 67-member slate" -- the Committee to Rebuild.

Thus, while the Bush slate for the convention in Detroit did manage to win in last May's primary, the Rebuild slate captured an overwhelming majority of the seats on the D.C. Republican Committee, the controlling body of the local party.

The convention delegates now say they plan to launch an all-out effort to get the convention to select Bush as Reagan's vice presidential running mate. But they face stiff opposition from Reaganites and other conservatives who want someone more ideologically akin to Reagan.

The delegation also plans to lobby the GOP's platform committee -- where the District has two representatives -- for an urban policy plank in the Republican platform.

According to most delegation members, acceptance or nonacceptance of an urban policy plank will be a key indicator of whether the conservative Reaganites or the more moderate forces will prevail to set the future national course of the GOP.

"I would hope the Republican Party might entertain some of our [urban policy] proposals," said attorney and Washington Diplomats owner Stephen I. Danzansky, one of the delegation's representatives on the platform committee.

"I think it will indicate whether Reagan is seeking to bring together a united party," Danzansky said.