NORTH TONAWANDA — In a city where 30 percent of voters are registered Republicans, the GOP’s success in Tuesday’s election left many party leaders still trying to catch their breath the day after landslide victories.

A deeper look at the results shows the scale of the Republican win was overwhelming:

The party’s mayoral candidate, Robert G. Ortt, took home 66 percent of the vote in a race against incumbent Democrat Lawrence V. Soos, according to unofficial results reported by the Niagara County Board of Elections. In the end, a GOP candidate will hold each of the five Council seats, as well as the mayor’s post, from Jan. 1 through 2011.

The average margin of victory for Common Council candidates was nearly 20 percentage points in the four races, with the race in the city’s 2nd Ward equaling the 2-to-1 margin seen in the mayor’s race.

Republicans also will hold all three of the city’s seats in the County Legislature beginning next year.

Party officials are researching whether the hold on each city office by one party has ever happened before in the city’s history, said City Republican Committee Chairman Bill Paton, who tried to quell any potential concerns about one-party control in North Tonawanda.

“It’s not going to be a Republican-run city; it’s going to be a city run by the people represented by the Republicans,” Paton said. “We’re going to listen to what [the people] have to say.”

The overall success in the mayor’s race along with the other races was surprising, Paton said. The party had done some polling that predicted GOP victories, but not to the degree that came to bear Tuesday, he said.

There was a sense the GOP could sweep the races, a notion that came in the feedback candidates received by going door-to-door during their campaigns, Paton said.

State Sen. George D. Maziarz, the county’s leading Republican figure, led the cheers during a GOP gathering in the Fairways at Deerwood restaurant after the polls closed.

“I think tonight may be the greatest night the Republican Party has ever had in North Tonawanda,” he told the crowd.

Maziarz is a city native.

Ortt, 30, received 4,748 votes to Soos’ 2,465, according to unofficial results, which also do not include absentee ballots. He is the current city clerk-treasurer, a position he was appointed to in April 2007 and which he ran unopposed for later that year.

Soos, 66, served as an alderman- at-large from 2002 through 2005 and defeated Republican Michael P. Carney in the 2005 campaign.

Soos’ margin of victory then was 212 votes, or about 2 percent.

Election figures show Ortt would have won without any votes on minor party lines, Paton said.

The candidate with the biggest margin this time, next to Ortt, was Richard L. Andres Jr., who defeated Democrat Jerome M. DiVirgilio in the 2nd Ward race.

Andres got 1,220 votes to Di- Virgilio’s 637.

The narrowest margin of victory came in the the race for 1st Ward alderman. There, incumbent Dennis M. Pasiak took home a victory over Robert W. Fritz by 271 votes, or 12 percentage points.

In the other races, 3rd Ward Alderwoman Nancy A. Donovan beat former alderman Dennis J. Barberio for a four-year, at-large seat on the Council. In the 3rd Ward race, Eric M. Zadzilka defeated Janet B. Zehr.

Compared with the 2005 election, there were 2,214 fewer votes cast in the mayor’s race this year.

There are 19,529 registered voters in the city — including 8,482 Democrats and 5,971 Republicans — according to the most recent figures from county elections officials.

Democrats make up 43 percent of voters, while Republicans make up 30 percent. About 17 percent of the total number of voters are not affiliated with a party.

Democrats outnumber Republicans in each of the city’s wards — 45 percent to 29 percent in the 1st; 44 to 29 in the 2nd; and 40 to 33 in the 3rd, according to the Elections Board.

Niagara County Republican Chairman Henry F. Wojtaszek, who called Tuesday’s margins “a very pleasant surprise,” said he believes the GOP was able to recruit better candidates than the Democrats.

Wojtaszek also credited the candidates’ hard work in door-to- door campaigning as a key to their success on Election Day.

“Each had some good ideas that they were able to convey to voters,” he said.

Niagara County Democratic Chairman Daniel Rivera characterized Tuesday night as “lousy” for Democrats across the state.

He called it a turnout issue and pointed to the Democrats’ loss of downstate county legislatures and the near-loss of Nassau County Executive Tom Suozzi.

“Our base was not riled and mobilized nearly as well as our opponents’,” Rivera said.

City Democratic Committee Chairman Mark Houghton could not be reached to comment.