When the big black headlines of the Abscam scandal suddenly tarnished seven congressmen and a U.S. senator, it seemed that their political careers were ruined, perhaps finished.

But the torrent of damaging pretrial publicity and the political fallout from it suggest there is a more enduring rule in American politics: an incumbent is an incumbent until proven guilty.

In south Philadelphia, 17 people are challenging incumbent Rep. Michael O. (Oz) Myers in the April 22 Democratic primary. Most of them jumped into the race at the last minute, after news reports that the congressman had been videotaped taking $50,000 in cash from undercover FBI agents.

But the Democratic ward leaders of Philadelphia have refused to desert Myers or Rep. Raymond F. Lederer, who also has been implicated in the Abscam operation. They rejected Mayor William Green's pronouncement that the two incumbents are "unelectable." They ignored the mayor's effort to handpick two city judges to run against the accused congressmen.

"I'm loyal to Oz and Ray," said city councilman James Tayoun. "I'll remain loyal until they're indicted and convicted. Then I'd have to bid them a fond farewell and go elsewhere."

Grand juries in Washington and Brooklyn began hearing evidence against seven House members and Sen. Harrison Williams (D-N.J.) after the news broke on Feb. 3. The first indictments aren't expected before mid-April.

At least for now, Tayoun's kind of loyalty seems to prevail in the home districts of the congressmen who allegedly promised to trade legislative favors for cash from a mythical Arab sheik. Despite concern that the publicity alone would destroy their political lives, the reelection hopes of most, if not all seven, seem alive and well.

For instance, Reps. Frank Thompson (D-N.J.) and John Murtha (D-Pa.) don't even have any primary opposition yet. Others like Myers and Rep. John M. Murphy (D-N.Y.) face plenty of opposition, but traditionally the presence of a great many candidates helps incumbents, whose hard core of support remains loyal as the challengers cut each other up.

State and local party leaders interviewed during the past week say they recognize political reality: the Abscam disclosures tend to make the incumbents more vulnerable. In Philadelphia and Florida, for example, debates about how to deal with the accused have fractured party unity.

Republican Party officials in Florida have made no public effort to dump Rep. Richard Kelly, who admitted stuffing $25,000 in cash into his pockets after his encounter with the FBI in January. But they are scurrying behind the scenes, trying to find a candidate to challenge Kelly in the September primary. "Someone other than Kelly has to run," one said simply.

David Glancey, chairman of the Democratic city committee in Philadelphia, said some of the ward leaders still supporting Myers and Lederer are practical "to the point of being immoral. They figure if they end up indicted and convicted the seat is as good as vacant and they'll get another bite of the apple -- the chance to pick their own candidate."

A look at the political fallout from Abscam uncovers a wide range of opinion about the alleged stars of the FBI's videotaping show, and about the political systems that produced them.

Marcia Duffy, acting executive director of the Democratic Party in South Carolina, said many people feel that Rep. John Jenrette, another of those named, "is a damn good congressman because he takes care of his people. Johnny has been in a lot of scrapes, but he always seems to come out of them." j

Alan Schafer, chairman of the Dillon County, S.C., Democratic Party and a Jenrette supporter, said he feels the incumbent will be tough to beat unless indicted and tried before the June 10 primary.

"He's got a lot of sympathy from the average voter," Schafer said. "He's been tried in the press for the last several years. If he's guilty of anything the Justice Department should give him his day in court, give him a chance to face his accusers. So far we've had big newspaper headlines and that's all."

On Friday, Jenrette's attorneys filed a court motion demanding a quick trial. They said the cloud over his reelection campaign could only be cleared by a speedy trial or an official apology.

A first-term state legislator, Hicks Harwell, is the only person who so far says he'll challenge the incumbent in the primary.

Harwell took the floor of the legislature last month to denounce, as a "redneck," a reporter who had described him as heavyset and a flashy dresser who drove a luxury car with a tune-playing horn.

In a recent phone interview, Harwell agreed he could be called flamboyant. He said he has a Mark V Continental that plays the love theme from Dr. Zhivago when he honks. He said he picked the song -- "Somewhere My Love" -- so he'd have an answer when his wife asked where he'd been.

Here's a closer look at the political situation in the districts of the House members named in news reports as targets of the Abscam investigation (Sen. Williams doesn't face reelection until 1982):

Pennsylvania: Philadelphia, which has had more than its share of political scandals, was stunned by the news that two of its congressmen and three members of the city council were under suspicion.

Reform-minded Mayor Green got out front in a hurry, then had to retreat. City party leader Glancey recalls, "It was not the best week I even had." But he said that Lederer and Myers weren't the only issue when ward leaders thumbed their noses at Green's handpicked judges. "There could have been a Jane Byrne factor, too," he said, referring to Green's unpopular efforts to lay off city police and firemen because of a financial crisis.

Another problem was having to go outside the city organization to find candidates. "There's a dearth of talent from which to pick people," Glancey said. The political machine of former mayor Frank Rizzo was "run by generals who didn't like lieutenants. They'd rather have all soldiers, and that has an effect on your pool of talent," he said.

Tim Savage, a ward leader in Lederer's third congressional district, said Mayor Green's effort to oust the incumbents was hamhanded. The meeting of district ward leaders was poorly attended, and Savage said he and a state representative disputed contentions that Lederer was unelectable and that Green's hand-picked candidate was the man for the job. "Lederer has a following and a reputation. He's probably the humblest guy I've ever met in politics," Savage said.

Last Monday night more than 700 people turned out for a Lederer fundraiser, his first public appearance since the scandal broke. He faces six little-known opponents in the primary three weeks from now. Two years ago he was unopposed.

Aides says Lederer is confident because he gives his district "plenty of service," from taking care of Social Security checks and garbage collection to getting a Navy contract that saved 3,000 jobs in the local shipyard.

Myers is facing stiffer opposition. A ward leader from the same district is among the challengers, and several Italian-American candidates threaten to split the white vote in the racially mixed south Philadelphia district, according to local experts.

The last time, Myers got less than 50 percent of the primary vote, but five other candidates split the rest so evenly that he won handily. The 36-year-old former longshoreman easily won the general election.

City Democratic leader Glancey said the party organizaiton is not lifting a finger to help the two accused incumbents. He added that he couldn't really explain the lack of success of the local Republican party, "We've been beating them over the head for 20 years. It's probably tough to find good Republican candidates. They probably see themselves as sacrificial lambs and say, Why bother?"

Murtha, the third Pennsylvania Democrat named in Abscam, has made no public appearances in his district, northeast of Pittsburgh, since the scandal broke. But he faces no primary opposition.

Florida -- Kelly, the only Republican involved in Abscam -- and the only member to acknowledge taking money -- has been a thorn in the side of the Republican Party in Florida for years, according to officials there.

Party chairman William Taylor, a Jacksonville insurance man, says Kelly's behavior reminds him of a man who once confounded an electrocardiogram machine because he was "wired upside down," Taylor said: "Well, what's normal for Dick Kelly is abnormal for everyone else."

"He's obnoxious, he's antagonistic, he's pugilistic, but put him on a stage and he comes across like the most sincere, convincing man. It's almost like he's two persons."

Taylor said the party leaders have been talking with Kelly, but so far have made no public move to oppose his reelection. "He's extremely well-liked by the people," he said. "All you here is, 'He votes right.'"

In the 1978 general election, Kelly won by only 51 percent to 49, and three well-financed Democrats are vying to oppose him this time. A Republican state senator from the eastern edge of the sprawling central Florida district is taking on Kelly in the primary.

Curt Kiser, now the House minority leader in Florida, started to run but dropped out, complaining that GOP leaders give him nothing but "lip service." About the situation today, Kiser said, "There's no doubt they're fumbling around. They don't know how to handle this, though they understand he can't win another general election.

"A lot of people told me how bad Kelly was, how he was an embarrassment, how he never did a thing for the party," Kiser said. "But he's on the Agriculture and Banking committees and I found out the interest groups there like the way he votes and give him lots of PAC [political action committee] money."

Kelly returns periodically to the district, where he is greeted at times with standing ovations at dinners and town meetings.

Republican leaders from his home area of Pasco County signed a resolution backing Kelly. Loyalty, they said," is a noble and Republican virtue."

Chairman Taylor summed it up: "Everyone thinks everyone else's congressman is a crook but theirs."

South Carolina: Jenrette ran unopposed in the last general election despite waves of publicity about grand jury investigations focusing on his activities.

Local papers say he's a good bet to win the primary again, unless the colorful Harwell captures the backing of some important district leaders.

The Charlotte, N. C., Observer quoted an influential local Democrat as saying the incumbent is still popular in the mostly rural district of northeastern South Carolina.

"They like ol' John. They can pick up the phone and call his office and get something done. These tobacco boys are running scared; they don't have too many friends and John knows tobacco," the Democractic leader said.

State Rep. Harwell said Jenrette should start dealing with the realities of his legal and personal problems: "The real issue is representing the district. It deserves someone voting and going to committee meetings."

John Napier, a former aide to popular Sen. Strom Thurmond, announced he would run in the Republican primary the week before Abscam broke. The 32-year-old lawyer notes that he knows something about ethical and financial dealings because of his work as minority counsel in writing the new Senate ethics code.

Jenrette, in the meantime, is getting a sympathetic response to his decision to seek treatment for a drinking problem, an aide said.

Ironically, his most serious political problem lately has been from the Carter White House, apparently because Jenrette hadn't yet endorsed the president's reelection bid. As a result, announcements about grants for Jenrette's district were bypassing the congressman's office and being made by the governor.

New York: Like Jenrette, Rep. John Murphy is used to seeing his name in headlines about government investigations. In a phone interview last week he said the controversy hasn't hurt him politically.

Local political leaders have expressed continued support. When he goes home for Saturday office hours on Staten Island, Murphy said, "People invariably volunteer: 'I'm with you all the way' or 'I don't believe this.'"

Murphy allegedly was videotaped with a Philadelphia lawyer discussing legislation with FBI undercover agents. But when he was offered a briefcase filled with $50,000, he declined and the attorney, Howard Criden, allegedly took the money.

Federal prosecutors have been trying -- unsuccessfully so far -- to reach an agreement with Criden's attorney to obtain his testimony in the Abscam cases. a

The 53-year-old Murphy is a West Point graduate who has represented the district since 1962. As chairman of the House Merchant Marine and Fisheries Committee, he is in a good position to obtain federal programs for his constituents.

"I gotta produce with dollars and cents," he said, ticking off a list of projects for the district ranging from a park system for the island to saving a hospital.

The New York primary isn't until September. In 1978, Murphy beat Thomas H. Stokes by 15 percentage points. Stokes is running again, as are several others, including Mary Codd, a city councilwoman from Staten Island.

In announcing her candidacy March 10, Codd said she would mention Abscam, but not as an important part of the campaign. A few minutes later, according to one published account, she couldn't resist adding: "But that doesn't mean that corruption will not be an issue in this campaign . . . Polictical victory has become a license to plunder the public treasury."

New Jersey: Rep. Frank Thompson, another committee chairman and veteran House member, faces no opposition yet in the June 3 primary.

In 1978, he beat a "Right to Life" candidate by 62 to 38 percent. That Republican contender has announced again as an opponent. So has a former Catholic priest who now works at a Gino's restaurant.

In his first appearance back in the district since he was mentioned in Abscam, the silver-haired 61-year-old "Thompsy" got a standing ovation from a large crowd at the Mercer County Senior Citizens Council.

State Republican leaders tried without success to lure a popular township mayor into challenging Thompson, who has been reelected every two years since 1954.