The Republican National Committee annnounced plans yesterday to spend $4.3 million more on a nationwide television advertising campaign to try to persuade voters to "Vote Republican -- For a Change" in November.

The Republicans have already spent about $4 million since last February broadcasting commercials in selected media markets, and GOP Chairman Bill Brock said yesterday that polls taken in those markets indicated that the commercials have had a dramatic effect on public opinion.

A total expenditure of more than $8 million in one campaign year on this kind of partisan television advertising is without precedent in American politics. The money spent on these commericals is not controlled by any of the legal limits on campaign spending.

Republicans" ads -- financed by the national committee and the House and Senate Republican campaign committees -- lambast the Democrats on charges of mismanaging the country's affair for 25 years while they controlled both houses of Congress. Some are clever dramatizations, others are direct commercial pitches.

According to both Brock and pollster Robert Teeter, whose firm, Market Opinion Research, tested the effectiveness of the commercials run earlier this year, they produce a dramatic change in voter attitudes in the areas where they are shown.

At a news conference yesterday, Brock said opinion shifted against the Democrats and toward the Republicans by from five to 20 percentage points in test markets where the commercials were shown.

Brock said the commercials -- 30 second spots -- are now being shown on network television, and will be until the second week of September. This phase of the ad campaign will cost $1.4 million, he said.

In the second and third weeks in October, the commercials will run in about 60 regional media markets, then in the last two weeks of the campaign a final $2 million worth of ads will appear on the major networks. By October, of course, the nation's airwaves will be saturated with political ads for the presidential candidates as well as local politicians.

Neither Republicans nor Democrats have ever put on a comparable ad campaign. In 1978 the Republicans bought $1 million worth of commercial time for congressional candidates.

The Republicans' commercials this year have already received wide recognition, particularly one featuring an actor closely resembling House Speaker Thomas P. (Tip) O'Neill Jr. in that dramatization, the O'Neill figure is driving a car whose passenger warns that it is running out of gas. No, no, the driver insists as they cruise past the last gas station. Then the car runs out of gas, and the O'Neill figure can't understand what happened.

At their news conference yesterday, the Republicans unveiled a new commercial that Brock said the most effective yet produced. It depicts a Baltimore printer, Jim Wilder, walking through an empty, silent plant, and saying: "I used to work here . . . Nearly a year ago they closed the plant for good. I'm one of the millions of people in this country who have lost their jobs . . . If the Democrats are good for working people how come so many people aren't working?"

Then an announcer comes on: "Let's get America working again. Vote Republican for a Change."

Rep. Guy Vander Jagt, chairman of the House campaign committee, described Wilders as a genuine unemployed worker who wanted to be a spokesman for people out of work. Responding to a question. Vander Jagt said Wilders had found a new job -- paying less than his old one -- two days after making the commercial.

Meanwhile, a political strategist for one of the many independent groups boosting Ronald Reagan's candidacy said the groups will fall far short of raising the $50 million they once thought they could.

Many of the people heading up the groups had little experience in raising money under the campaign finance laws enacted in recent years and didn't appreciate the difficult in collecting huge sums, according to David Keene, a strategist for the Victory Fund.

"Their intial guesses of what they thought they could raise were out-landish," Keene, formerly political director of George Bush's presidential campaign, told a news conference.

At least five "independent expenditure" groups are working to raise money for Reagan. The most ambitious of them, Americans for Change, headed by Sen. Harrison Schmitt (R-N.M.), has said it alone will raise from $20 million to $30 million. This would almost equal the $29.4 million in federal campaign funds that major party nominees receive and are limited to spending under federal law.

The groups could do so by exploiting a controversial Supreme Court ruling allowing unlimited spending by committees as long as they have no contact with a campaign.

The Victory Fund, a creation of the Nationl Conservative Political Action Committee, has raised $400,000 and expects to spend about $1 million during the fall campaign.

Keene said most of it will be targeted at President Carter's political base -- the South. The group, he said, intends to issue a series of television, radio and newspaper advertisements designed to "raise the feeling that it isn't only acceptable but it is wise to vote against Jimmy Carter in the South."

The activity will be concentrated in Alabama, Louisiana, Mississippi, and the panhandle of Florida, all areas where Carter exhibited weakness in 1976.

The Reagan campaign will be unable to spend large amounts of money in these areas, Keene said, adding. "We will be filling a void that may otherwise not be filled, reaching voters who may not otherwise be reached."