Rep. Jack Edwards (R-Ala.) has been invoked, quoted, photographed and praised so many times by his two would-be successors that many voters may wonder if he really has retired.

For 20 years, the amiable conservative has been one of the most enduring and beloved politicians in this area of timberlands, pecan groves and sandy Gulf Coast beaches. Now, in a political landscape that stretches from conservative to ultraconservative, Republican H.L. (Sonny) Callahan and Democrat Frank McRight are vying over who is Edwards' rightful heir.

Similar battles are being waged in 26 other so-called "open" congressional districts where no incumbent is running. Absence of an incumbent makes these contests more susceptible to national trends and to the margin in the presidential race, and historically these have been the seats most likely to change hands in an election.

Republican and Democratic strategists view the 27 open seats as a key battleground in the struggle for control of the 99th Congress. Democrats controlled the last House by a 99-seat margin. The Republicans are eager to reclaim at least the 26 seats they lost to the Democrats in November 1982, in hopes that they can reconstitute the 1981-82 coalition of Republicans and conservative Democrats that approved President Reagan's economic program over the objections of the House's Democratic leaders.

The Democrats are equally intent on preserving their margin and have focused much energy on the open seats.

"There are two key groups this year: our freshmen and our open seats," said a Democratic strategist. "Some of our freshmen are likely to lose, but we hope to offset those losses by gains in open seats."

The Democrats base their optimism on the fact that the Republicans have more to protect: 14 of the open seats were held by Republicans and 13 by Democrats. The Democrats say they can pick up three or four of the Republican open seats.

The Republicans, for their part, figure they can hold all but two of their open seats. They also hope to pick up five or six of the previously Democratic open seats.

Republican and Democratic strategists agree that at least two Republican seats are likely to change hands.

Rep. Phil Gramm (R-Tex.), who was a Democrat until he switched parties nearly two years ago, gave up his seat to run for the Senate. He is the only Republican ever to have represented the College Station district. Both parties agree that Democrat Dan Kubiak, a former state representative, is likely to reclaim it by beating Republican Joe Barton, an engineer.

The seat being vacated by Rep. Ed Bethune (R-Ark.) in the district that includes Little Rock is also expected to go to a Democrat, flamboyant Pulaski County Sheriff Tommy Robinson. His opponent, state Rep. Judy Petty, hurt her cause when she told the Republican National Convention that there are "some things worse than war."

Democratic officials say they also have a good shot at the seats being vacated by Edwards and by Republican Reps. Dan Marriott (Utah), Larry Winn Jr. (Kan.) and James G. Martin (N.C.).

Republican officials are hoping to win in districts represented during the last Congress by Democratic Reps. Norman E. D'Amours (N.H.), who is a Senate candidate this year; Tom Harkin (Iowa), also a Senate candidate; Richard L. Ottinger (N.Y.), Ray Kogovsek (Colo.) and Kent R. Hance (Tex.).

One of the closest races is for what Mobilians call "Jack Edwards' seat."

Republican Callahan has placed himself squarely within the traditions of Edwards, who endorsed him even before the Republican primary. Callahan's theme is that a Republican will have access to the White House and therefore can serve the district better. He has grabbed the Reagan bandwagon -- the 1st District gave Reagan his strongest showing in Alabama in 1980 -- and has tried to tie McRight to Democratic presidential candidate Walter F. Mondale.

McRight, however, is having none of it. A Carter-Mondale campaign worker in 1980, this time he has avoided endorsing Mondale and declines even to say whether he will vote for the Democratic ticket. When Mondale was considering campaigning in the district, McRight threatened not to show up. Mondale decided not to go.

While promising effective constituent services, as Edwards did, McRight's main theme has been the need for fresh leadership in Washington. This is none-too-veiled criticism of his Republican opponent, who has ties to a group of local officials who were recently indicted on extortion charges.

Early on, Callahan was considered a shoo-in. But he has committed several political blunders. During the primary he did not show up at several candidate events. Later he ran a television commercial that, in effect, made fun of McRight's balding pate. The stunt backfired, with dozens of indignant people, bald or balding, coming up to McRight or calling his headquarters and pledging their support.

McRight also has had some political luck. A black independent who was running for the seat backed out recently and threw his support to McRight.

New Hampshire's Democratic challenger, Dudley Dudley, has had no such luck in her race against conservative Republican Robert C. Smith to succeed D'Amours. Smith lost to D'Amours in l982 but is considered the likely victor in the conservative Manchester-dominated district.

A descendant of Daniel Webster, the articulate and hard-working Dudley is considered much more liberal than many voters in her district, where Reagan has a 35 percent lead in the polls. The district's largest newspaper, the right-wing Manchester Union-Leader, has gone after her in its editorials from the day she announced.

Dudley, who organized a draft for Sen. Edward M. Kennedy (D-Mass.) in the 1980 presidential election, is downplaying her liberal image these days. She describes herself instead as a "fighter" for New Hampshire, an environmentalist who strongly opposes the Seabrook nuclear power plant and an experienced candidate. She is in favor, she says, of a strong national defense but also endorses a nuclear freeze.

Unlike Alabama's Callahan, Dudley has not received a rousing endorsement from the lawmaker she is trying to replace. In fact, D'Amours, who is in a tough Senate fight, seems to be staying as far away from the unabashedly liberal Dudley as possible.

Her opponent, mild-mannered real estate agent Bob Smith, describes himself as the quintessential small-town conservative Republican. He has campaigned for the seat twice before, promises to provide the sort of services D'Amours did and goes from door to door with a copy of the Constitution and a cookbook by his wife, Mary Jo.

Smith is running "to the right of Ronald Reagan," according to one Manchester Republican, but he says he disagrees with Reagan on issues important to New Hampshire voters and supports cleanup of acid rain and toxic wastes.