The signs along the road, amid the palm trees and strip shopping centers, announce: "For Congress, Reid Hughes. A Real Democrat."

That theme has brought virtually every national Democratic interest group stampeding into Florida's 4th Congressional District in the last few weeks. The bait: the chance to defeat one of the most influential members of the "boll weevil" caucus, Rep. William V. Chappell Jr. (D.), in today's primary runoff.

Environmentalists were among the first to embrace Hughes, a prominent local conservationist who surprised the odds-makers by forcing the seven-term Chappell into a runoff.

They were soon joined by other groups angered by the Reagan programs that Chappell and other conservative Democrats helped pass in the House: the National Organization for Women, the National Education Association, the AFL-CIO, PeacePAC, the Communications Workers of America, senior citizens groups and others.

Chappell has enjoyed a similar outpouring of support from the "other side," getting hefty campaign contributions from defense contractors, developers, banks, the National Rifle Association and the Boll Weevil Political Action Committee.

"Boll weevil" is a term for Democrats who have supported President Reagan's programs.

In the process, the environmentalists have seen their concerns about water pollution and land erosion slip into the background, but they still have much at stake in this race. It is a test of their 1982 Southern Strategy, and a training ground for the general election.

The League of Conservation Voters, the richest and best organized of the environmental political action committees, has poured money and manpower into burgeoning Sunbelt states like Florida and Texas where redistricting has created new congressional seats and diluted the bases of entrenched incumbents.

The idea is that environmentalists, and grass-roots movements in general, have a better chance of capturing a new or redrawn district than uprooting an incumbent. Florida is especially fertile ground for environmentalists because of growing public concern over developmental threats to the state's prized natural areas.

Florida gained four congressional seats this year, and Chappell and Republican Rep. Bill McCollum of Orlando lost key precincts in the reshuffling. Hoping to capitalize on the shake-up, the League of Conservation Voters targeted the Chappell and McCollum races, and two new districts in the Gainesville and Tampa areas. In each race they are backing local politicians or civic leaders who have supported environmental causes.

The special lure in Chappell's district is that he has the lowest environmental voting record in the Florida House delegation (6 on a scale of 100, according to the conservation league's index), largely because of his House Appropriations Committee votes for costly water development projects.

Here, the league has mounted a door-to-door canvass that aims to pull 2,000 pro-Hughes voters to the polls today--enough to provide a victory margin, according to strategists for both candidates. Hughes ran surprisingly close to Chappell in the Sept. 7 primary, receiving 45 percent of the vote to Chappell's 48.

The canvassers are young environmentalists from around Florida, trained in crash sessions led by league organizers in a cramped room in the back of Hughes' headquarters. They work long hours for minimum pay, door-knocking from early morning until 9 p.m.

At each doorstep, they prod voters to consider environmental concerns. Then they note that Chappell has "the worst environmental voting record in Florida," and wind up with a pitch for Hughes. Those who respond positively will get follow-up phone calls and, if needed, a ride to the polls on Tuesday.

Environmentalists now account for one-third of Hughes' campaign field staff of about 100, including the League of Conservationists canvassers and local members of the Sierra Club, who man phone banks.

After the polls close today, they will be deployed for the general election--in Orlando, for State Rep. Dick Batchelor, McCollum's Democratic opponent, and in the new Tampa district, for state Rep. George Sheldon.

A clean sweep on Nov. 2 would give the environmentalists four new supporters in the House. What about a washout?

"There's always 1984," says a league strategist.