Buffalo, N.Y. — President Reagan swept into Democratic territory in upstate New York yesterday, flexing his political muscle as polls show his lead increasing to nearly 20 points.
The President targeted Italians, Poles, and Roman Catholics in Buffalo when he dedicated the Santa Maria Towers, a senior-citizen and handicapped housing project. The project was built with funds from the federal government and local Catholic and Italian groups.
''He is in the unique position historically of having a tremendous lead in half the country,'' says Gerald M. Goldhaber of Goldhaber's Research Associates and a professor at the State University of New York at Buffalo.
''He doesn't need to spend as much time within his territory (mostly west of the Mississippi). So he can go after Mondale in (Democratic) strongholds.
''Mondale has to campaign in 50 states. But he also has to shore up his support, and thus has to spend time in his base.''
Leaders in both parties in Erie County do not expect Reagan to win here. The county, which includes Buffalo, produced the biggest margin for Carter in New York State in 1980, and was the only county in the nation to give Carter more votes in 1980 than in '76, says one local politician.
Democrats outnumber Republicans almost 4 to 1, although the county executive, Ed Rutkowski, is a Republican.
''The President has never shied away from a challenge,'' says Mr. Rutkowski. He says he hopes the President can cut losses here.
Reagan's speech at the Santa Maria Towers on Buffalo's West Side, emphasized that America is ''moving forward . . . into a brighter future.'' In a city with a June unemployment rate of 8.3 percent he talked about the economy, harking back to the double-digit inflation of four years ago.
The President said it was time to put the country ''back into the hands of the people.''
''And that's exactly what we've been trying to do with the strongest economic expansion in 40 years, and inflation all the way down from 12.4 percent to 4.1 percent. But we must remove the remaining roadblocks to growth and jobs - without inflation - so a city like Buffalo will finally enjoy all the warmth from the sunlight of prosperity.''
The President criticized Mr. Mondale's proposal for reducing the deficit, which includes a tax increase. He used words from Franklin Delano Roosevelt: ''The only way to keep the government out of the red is to keep the people out of the red.'' The audience cheered.
''I like Mr. Reagan's image and presence,'' said Sal Lombardi, a doctor who came to see the President.
''This President gives the voters a better feeling about themselves and the country,'' says Mr. Rutkowski.
It is this emphasis on charisma that worries some opponents.
Democratic leader Joseph Crangle would rather have the election focus on the economy in the Buffalo area. He points to a projected deficit in the Erie County budget, and says that cuts in social services at the federal level have put a heavy burden on state and local governments.
The number of people on home relief, the state program that picks up people who have run out of unemployment benefits, has increased 137 percent since Mr. Reagan took office.
Rutkowski, who was on the podium with Reagan yesterday blames the county's woes on state government, which he says ''dumps programs'' on the backs of counties.
And there are other reasons why Reagan visited upstate, says Dr. Goldhaber. New York is the second largest state, and Mr. Reagan won here by just 165,000 votes in the 1980 election. Polls show the contest in this state very close.
And at a time when New York Gov. Mario M. Cuomo and Democratic vice-presidential candidate Geraldine A. Ferraro are engaged in a debate over politics and religion with the New York Archbishop John J. O'Conner, Reagan may find it advantageous to court Catholic voters, says Goldhaber.
Still, there are plenty of voters who don't favor the President.
''Mr. Reagan is quite popular and a good communicator,'' says Daniel Acker, president of the local NAACP branch. ''But he has helped the rich, and there's been an increase of hunger in the Buffalo area.''
One retired factory worker, a Republican who asked that his name not be used, said he wouldn't vote for Mr. Reagan this year. ''I don't like what he did to senior citizens.''