In Illinois, a wealthy real estate developer from California has spent more than $419,000 of his own money to defeat Sen. Charles H. Percy (R-Ill.) with billboards and televised ads denouncing him as a chameleon.

In Texas, the National Rifle Association has put up a quarter of a million dollars to help Rep. Phil Gramm (R-Tex.) win a Senate seat.

In other states and districts, from Massachusetts to Montana, the American Medical Association's political action committee (PAC) has saturated the cable television market in an ambitious experiment to promote five House and Senate candidates.

The campaigns are all part of a relatively new and apparently burgeoning phenomenon in American politics: independent expenditures that can have an impact at crucial periods in a campaign without a word in advance to the candidate and his advisers -- or their opposition.

Because these expenditures are made independently, there is no limit on the amount that can be spent. By law, individuals and PACs are limited in the amount that they can contribute directly to a candidate.

Independent expenditures have been made in the past by PACs and individuals. The National Conservative Political Action Committee (NCPAC), for example, spent millions on negative ads in past elections trying to defeat liberal Democrats. But it appears this year that more PACs are trying to accentuate the positive, and are spending a larger share of the money on such free-lance efforts.

Randy Moorhead of the National Association of Realtors said that independent expenditures by his organization are bigger than ever and that he expects them to keep growing in the years ahead.

"A larger portion of the money can be used wisely," Moorhead said, in contrast to the cash contributions of $5,000-per-election that PACs can give to a congressional candidate. He predicted that independent spending would become even more significant if Congress should enact new restrictions on the amount of PAC money that a candidate can accept.

Realtors PAC has just paid out $49,000 for a series of television ads starting in the Baltimore area this week on behalf of Republican candidate Helen Delich Bentley's tightly contested effort to unseat Rep. Clarence D. Long (D-Md.). The National Association of Realtors' independent expenditures committee is considering last-minute television commercials on behalf of several other candidates, Moorhead indicated.

The title of biggest individual spender already has been nailed down by a California real estate developer named Michael Goland, who began his anti-Percy crusade last year with a $1,325 check to Congressional Quarterly for a "research package on Senator Percy's voting record."

Since then, Goland, who has now taken a Chicago apartment, has spent another $418,254 on a series of attention-getting commercials, brochures and billboards. One commercial shows a chameleon crawling across the TV screen while an announcer declares: "We haven't learned Percy's true colors, but we have learned that the U.S. Senate is no place for a chameleon."

Aides to Percy, who is chairman of the Senate Foreign Relations Committee, claim that the 37-year-old Goland's opposition stems from chagrin over Percy's voting record on Israel.

Goland could not be reached for comment yesterday, but he has denied the claim in interviews with Chicago reporters, dismissing it as a "Percy-created smokescreen."

Percy aides maintain that they are not worried by Goland's attacks, which they dismiss as inaccurate, but they also have filed a complaint with the Federal Election Commission asserting that Goland's pre-primary expenditures were not genuinely "independent." They also have sought to discourage Illinois television and radio stations from airing Goland's commercials.

Independent spending on Senate and House candidates in the 1981-82 election cycle totaled $5.7 million, with about 80 percent of that going for the kind of "negative campaigns" made famous by NCPAC. This year, NCPAC appears to be concentrating on promoting President Reagan.

Perhaps more typical this year is AMPAC, which says it is spending its money to promote favored candidates rather than to tear down incumbents they would like to see defeated.

AMPAC officials say they began with candidates whom their member-doctors favored and selected five from areas where they felt they could use the inexpensive cable television market most effectively.

As a result, for almost two weeks now, viewers of the financial news and sports programming networks in the Tulsa area have been watching 30-second spots promoting the embattled chairman of the House Budget Committee, Rep. James R. Jones (D-Okla.).

In Montana, where a 30-second cable-television spot costs just $10 a pop, audiences have been watching an "Old West" commercial touting Sen. Max Baucus (D-Mont.) about five or six times a day.

Other beneficiaries of AMPAC's $85,000 television campaign include Reps. Manuel Lujan Jr. (R-N.M.), Herbert H. Bateman (R-Va.) and Lewis Crampton, the Republican challenger in Massachusetts' 10th District.

The medical group also is running full-page ads for Sen. Roger W. Jepsen (R-Iowa) this week in every Iowa daily newspaper outside Des Moines.

For Rep. Thomas A. Luken (D-Ohio), it is "setting up phone banks, calling anyone over 62 years old, asking them their voting preferences, and whether we can send them an absentee ballot," AMPAC said.

According to FEC reports, AMPAC spent $211,624 in 1981-82 in the independent category. Officials say the total this time will be between $300,000 and $325,000.

Similarly, a spokesman for the NRA's Political Victory Fund estimated that its independent spending will be $300,000 to $400,000, compared to $232,350 in 1981-82.

"The Gramm race is very important to us," an NRA spokesman said of its heavy investment in Texas on billboards, radio ads, bumper stickers and staffers. "He's one of the strongest pro-gun, pro-hunting supporters in Congress . . . . And his opponent state Sen. Lloyd Doggett is distinctly anti-gun, a thorn in the side."