President Reagan's "nonpartisan" speech on the economy left the Democrats muttering in frustration last night, but may not have helped the Republicans much in the closing stage of the midterm campaign.

The speech was planned last week when White House aides feared that last Friday's news of double-digit unemployment would devastate their election prospects. First readings by pollsters of both parties indicate it has not had that effect.

Democrats hoped that last Friday's news that unemployment had passed 10 percent for the first time since the Great Depression would trigger a landslide of support for their candidates.

Apparently, it did not. Republican pollster Robert Teeter and Democratic pollster Peter D. Hart both said yesterday that surveys tracking voter attitudes in the past five days do not show any significant change.

"None of our candidates is in worse shape than a week ago," Teeter said. "I can't see that there's been a dramatic turnaround," Hart agreed. "You have a situation where 30 percent of the people are very concerned about the threat of layoffs, but there's been no real change in Reagan's job rating or the confidence or lack of confidence in his economic plan."

Two senior Republican strategists, who declined to be quoted by name, added the information that there had been a brief, sharp dip on Friday and Saturday--when the unemployment news was fresh -- but then polls had returned to their previous tracks.

John E. Merriam, who monitors media coverage in his Issues Management Letter, said that economic news had dominated the press and television in recent weeks but that -- thanks to the sharp cuts in interest rates and the stock market boom -- the ratio of good to bad news had increased from Reagan's point of view.

Under those circumstances, some analysts thought Reagan's speech a case of overkill. Others said that in trying to portray a brightening economic picture in the Oval Office address carried live by two networks, Reagan risked damage to his own credibility and a deeper skepticism about his party.

A Washington Post-ABC News poll, taken last week, showed 57 percent of the voters believe the country is headed down the "wrong track" and 61 percent feel they are worse off than they were when Reagan became president.

Reagan did his best to persuade them otherwise, but in claiming "important progress" on every economic problem but unemployment, he left himself open to the countercharge from Democrats like party chairman Charles T. Manatt that he and his party are "out of touch" with the reality of most people's lives.

And that could be politically costly to Republican candidates. Polls show that the main reason most voters are leaning to the Democrats is the fear that Republicans are insensitive and unresponsive to the problems of the jobless and the needy.

Reagan tackled that problem head-on, reading emotionally a letter from an unemployed Selma, Ala., woman and recalling his own family's experience with layoffs in the Great Depression. But Sen. Donald W. Riegle Jr. (D-Mich.), the opposition's designated spokesman, said the Reagan administration is dominated by "millionaires who have no understanding of what life is like for average people."

Manatt, who organized his own media blitz last Friday when unemployment hit 10.1 percent, criticized the NBC and CBS networks for having the "questionable judgment" to air the president's address in free prime time without providing a comparable response from the Democrats. Calling it "a message of no news and no ideas," he said the networks should bill the Republicans $500,000 for advertising time. CBS planned to put on four prominent Democrats, including Riegle and former vice president Walter F. Mondale and a union president at 11:30 p.m., four hours after Reagan spoke.

NBC squeezed in six minutes of Riegle's 15-minute response between the end of Reagan's speech and the start of the World Series telecast.

The Cable News Network was to carry both the Reagan speech and the full Riegle response. The ABC network carried neither.

Reagan, plainly intent on taking an active role in the campaign, made a minimal effort to disguise the partisan content of last night's address. It closed with the same catch phrase about "staying the course" that the Republicans have used in their multimillion-dollar advertising campaign.

On Thursday and next Monday, he is making speeches via satellite to a series of Republican fund-raising dinners, and before Election Day, he is expected to visit Nebraska, Illinois, Montana, Nevada and California for personal campaigning. All five states have close senatorial and/or gubernatorial races. New Mexico and Utah may be added to the list if the Republican senators there look like they need help.

The question, raised by people in both parties, is whether any speech or other ordinary news event can have much impact on an election now only 19 days away.

The experience of past elections is that voters form their basic attitudes over a long period of time and then apply them to the candidate choices during the closing weeks of the campaign.

Particularly is that the case when the dominant issue is one of economics, where people rely on their everyday experiences as a guide much more than they rely on any outside authority, including the president.

That is why Democrats said -- and Republicans conceded -- a few weeks ago that the "pattern was set" for the midterm election when the economy failed to muster the summer pickup that the administration had hoped for and predicted.