Day-by-day polling used experimentally by the Republican Party helped maintain its Senate majority in last Tuesday's elections, when seven GOP incumbents and one challenger won extremely close races.

The Republicans have won 19 Senate seats in 1980 and 1982 races where their candidates received less than 53 percent of the votes. Democrats have won four.

Had those numbers been reversed, Democrats would have held a 61-to-39 Senate majority and the "Reagan revolution" in budget, tax and defense policy would have been no more than a gleam in the president's eye. Instead, the Republicans still hold a 54-to-46 majority to offset an enlarged 267-to-166 Democratic majority in the House.

A major factor in winning these squeakers, according to those on both sides in these campaigns, has been a Republican effort to monitor the closing stages of these very tight contests through daily "tracking polls." This year, the Republican Senatorial Campaign Committee headed by Sen. Bob Packwood (R-Ore.) invested more than a half-million dollars in "tracking" 13 contests expected to be close.

Nationally, it alerted Packwood and his staff in mid-October to the danger of lethargy and a disproportionately low turnout among Republican voters. As a result, they shifted $1.3 million into a direct-mail appeal to 7 million households for their voters to turn out to save President Reagan's Senate majority.

The best example of the impact of the Republicans' "tracking polling" came in Missouri, where campaign managers for Republican Sen. John C. Danforth and his Democratic challenger, state Sen. Harriett Woods, said they believe the "intelligence advantage" this gave Danforth may have made the difference in his retaining his seat by only 27,000 votes out of 1.5 million cast.

"There is a danger of oversteering a campaign by reacting to every blip in the polls," said Alex Netchvolodoff, Danforth's administrative assistant. "But it is vital to know if you are moving up or down, so you can adjust your campaign."

Woods' campaign manager, Jody Newman, shook her head when she saw the chart of the race accompanying this article, which shows Woods catching and passing Danforth on the Thursday and Friday before the election, and then dropping sharply. "If we had had that information," she said, "we might have won."

Vincent J. Breglio, a professional pollster and executive director of the Republican Senatorial Campaign Committee, persuaded Packwood to invest in the "tracking polls" and include Missouri in his "tracking states."

In standard political polls, at least 500 people are usually interviewed in a short period in a state the size of Missouri. In "tracking polls," only 150 to 200 people are interviewed by phone on any evening. Because the chances of a sampling error or statistical variation are so high in a survey that small, three nights of polling results are accumulated to produce a larger sample size.

As the polling continues, night after night, the oldest returns are tossed out and the freshest added, to construct a rolling average. "Tracking" polls are still less accurate than a large sample taken in a single day or two, but they help chart trends that can be the key in the late stages of a close race.

Breglio said he regarded the 1982 tracking as "an experiment" which paid dividends in Missouri and several other close contests. But, he added, "this was really a dry-run for us for 1984," when, unlike this year, Republicans will have more Senate seats at stake than the Democrats.

Breglio picked Missouri even though Danforth was widely regarded as a solid favorite with a large lead in early opinion polls and campaign funds. But Missouri is a Democratic state, and Woods, though a novice statewide, had a strong political base in the St. Louis area and had shown herself a resourceful campaigner.

Robert Teeter, whose polling firm was hired to track this race for the Republicans, reported Oct. 11 that Danforth had a 50-to-39 percent lead. Two days later, on the evening President Reagan made his nationally televised address on the economy, the tracking showed Danforth holding a 52-to-37 edge.

But in Missouri, as in other places across the country where Breglio was tracking, there was a sudden surge of support for the Democrats around Oct. 13-18, when the Republicans became seriously worried they might lose their Senate majority.

Breglio, a conservative and Reagan loyalist, described the phenomenon as "Democrats coming home." Netchvolodoff, like his counterparts working for other moderate Republican senators in very close races, said, "The president's speech had a bad effect. He told people to choose sides between his way and any alternative, and they didn't like the choice."

Teeter and others had urged Danforth to launch a preemptive strike against Woods by emphasizing her liberal legislative record and views to the state's nominally Democratic but conservative small-town and rural voters.

But Danforth, an ordained Episcopal minister and overseer of charities funded by his family's Ralston-Purina fortune, wanted a high-road, positive campaign. Netchvolodoff characterized as "soft" Danforth's television spots, designed by Washington film-maker Charles Guggenheim to show his compassion and understanding.

Woods' campaign was anything but soft. The first 10 seconds of her toughest ad, excerpted from Danforth's ads, showed him talking about concern for the jobless, the elderly, the young. The film froze on his face in mid-sentence, over which was superimposed a listing of votes designed to show Danforth gutting programs on which those people depend.

"The message," said Netchvolodoff, "was that Danforth is rich, Danforth is a hypocrite and Danforth doesn't care."

The effect was dramatic. By Oct. 15, the tracking showed Danforth's lead down to three points. A St. Louis Globe-Democrat poll showed the race dead even.

But Woods was running out of money and had to pull her spots off the air on Oct. 15. Looking later at the Republicans' tracking, Woods' pollster, Irwin (Tubby) Harrison said, "I can't prove it, of course, but I really do believe if we had been able to stay on the air continually, we would have passed him in mid-October and won the race before he had time to get his new commercials on the air."

The tracking showed Woods losing ground as soon as her commercials came off the air. On Oct. 17, campaign manager Netchvolodoff, pollster Teeter and ad man Guggenheim met in St. Louis with Danforth and some of his political advisers.

By the rulings of the Federal Election Commission, neither Teeter nor the Republican Senatorial Campaign Committee staff could give Danforth exact figures from tracking polls without having it count as an in-kind contribution to be deducted from the limited amount the GOP could spend on Danforth.

But they could describe the trends. Once again, Danforth refused to attack Woods personally, but he approved a series of ads "with some edge to them," as Netchvolodoff put it, comparing his and Woods' positions on issues.

While Guggenheim was rushing those ads through production, Woods used a fresh flow of contributions prompted by the Globe-Democrat poll to get back on television Oct. 19, banging away at Danforth. Once again, she quickly closed on him. By the time his new ads began Oct. 21, tracking showed the race a tossup.

On Oct. 29, the Globe-Democrat published its final poll, showing Woods 4 points ahead, and that evening, the tracking poll also showed her in front for the first time. But on the night before, Danforth put his last new ads on the air.

"We called the new spot 'Blurred,' " Netchvolodoff said. "It started out with an out-of-focus picture of Mrs. Woods, and the announcer said, in effect, Missourians don't really know much about the person who might be their next senator. They don't know that she thinks the Social Security system will mend itself, that she would undo almost all the budget cuts of the past two years, that she is opposed to the balanced-budget amendment, that she wants to cancel the third year of the tax cut, and that she would favor a $250 billion tax increase by sunsetting all the exemptions in the tax code. At the end of the ad, her photo was in focus, and the announcer said, in effect, vote for Sen. Danforth. You know where he stands."

Those assertions, which the Woods campaign disputes but did not have ads to answer, apparently had their effect. From Oct. 29 to 31, tracking showed Woods going steadily down and Danforth moving up. Woods' campaign manager said, "We could feel it slipping away from us, but we just didn't have anything left for a closing spurt."

Woods' pollster Harrison said he was "envious" of the Republican tracking polls. "We would talk every day in our campaign about what we ought to be doing, but we only had money for two polls all fall, so we were constantly looking back at data 10 days old, and trying to guess where and how it might have changed," he said. "We just didn't have what they had."