A seat was reserved for the Rev. Perry Smith III at the National Black Republican Council dinner at the Shoreham last Wednesday night, and again for lunch the next day with Vice President Bush.

But Smith, the black Baptist minister from Prince George's County whose conversion to the GOP last spring was hailed by national party chairman Richard Richards as "one of the most significant things to happen to the Republican Party," declined both invitations at the last minute.

As a Republican candidate for Congress in Maryland's Fifth District, Smith had been feted at the White House four times since he became a Republican last February, and was among the handful of black GOP congressional hopefuls invited to the Wednesday dinner to celebrate what was expected to be his easy victory the day before.

But despite the blessings of national and state party leaders, Smith apparently forgot to woo the predominantly white rank-and-file Republicans in the district, and lost the election to William P. Guthrie, a white 29-year-old graduate student who had no political organization and spent less than $1,000 on the campaign. The vote was 5,325 for Guthrie and 3,227 for Smith.

"Socialization with the brass was not going to win the election," said Virginia Kellogg, a black Republican who is active in the county party. "I think it was a lack of organization. It was assuming too much."

At Smith's first luncheon with the national party leaders last spring, while the television cameras rolled, Richard Richards, chairman of the Republican National Committee, said that "firm commitments had already been made" to throw the weight of the cash-flush party behind Smith's unlikely bid to unseat Democrat Rep. Steny H. Hoyer.

As recently as primary day, Richards met with a concerned Smith and state party chairman Allan C. Levey to talk about the promised support. Smith raised $26,252 for his campaign, including $5,000 from the national committee, and said that Richards had promised that once the nomination was secured at least $38,000 more would be committed between the committee and the congressional campaign committee.

Yet all that Smith received from the party bigwigs, according to one of his supporters, was "$5,000 and a lot of advice."

But national committee spokesman Bill Greener denied suggestions by some county Democrats that Smith had been used.

"We have absolutely no apologies to make for supporting Perry Smith. We were confident that he was going to win. We were very surprised," Greener said. "Obviously, the campaign didn't execute to the degree that I'm sure they wanted it to."

"I assumed they were covering their bases, but somewhere along the line he forgot about the primary," said Levey.

Smith worked on the coffee, tea and forum circuit, but according to a Republican source: "They did more black teas and coffees than they did white ones."

Smith's campaign chairman, finance chairman and finance director did not come on board until late July, and his first paid staffer, finance director Dennis Parovek, did not start work until August. Smith had set a goal of registering 10,000 black Republicans when he switched allegiance from the Democratic Party, but by the May 14 deadline only 219 changes of party registration had been made, according to the Prince George's board of elections.

Local Republican stalwarts said that Smith refused to collaborate with countywide GOP candidates.

"We tried to get him on," said Ann Shoch, who with the support of the mainstream Republicans defeated William Goodman for the county executive nomination. "I asked John Burcham a longtime party stalwart and Smith's campaign chairman . We did everything but hit him over the head."

"He really needed us more than we needed him, but he didn't see that," added Shoch, saying that she was "crushed" by Smith's loss.

Smith refused to comment on his loss other than to say that he was counsulting with advisers about "some messy things that went down" on election day. He expressed bitterness at what he called a lack of press coverage of the black community.

"I don't think the press has been very kind to us," he said.

Guthrie called his victory "a reaffirmation of our peoples' faith in America and in our President Reagan." The doctoral candidate, who had no poll workers and who stayed home on election day, had been prepared to lose last Tuesday. Now, buoyed by his surprise victory, he is considering mounting a campaign against the formidable Hoyer.

"I can't see where my chances of winning the general [election] are any worse than my chances were in the primary," he said.