For several years now, corporations and other wealthy interests have made ever-larger campaign contributions, gifts and sponsored trips part of the culture of Capitol Hill. But now, with fresh guilty pleas by a lawmaker and a public relations executive, federal prosecutors -- and perhaps average voters -- may be concluding that the commingling of money and politics has gone too far.

After years in which big-dollar dealings have come to dominate the interaction between lobbyists and lawmakers, both sides are now facing what could be a wave of prosecutions in the courts and an uprising at the ballot box. Extreme examples of the new business-as-usual are no longer tolerated.

Republicans, who control the White House and Congress, are most vulnerable to this wave. But pollsters say that voters think less of both political parties the more prominent the issue of corruption in Washington becomes, and that incumbents generally could feel the heat of citizen outrage if the two latest guilty pleas multiply in coming months.

No fewer than seven lawmakers, including a Democrat, have been indicted, have pleaded guilty or are under investigation for improper conduct such as conspiracy, securities fraud and improper campaign donations. Congress's approval ratings have fallen off the table, in some measure because of headlines about these scandals.

"The indictments and the investigations have strengthened the feeling that people have that in fact there's too much money in Washington and that the money is being used to influence official decisions," said William McInturff, a Republican pollster with Public Opinion Strategies. "Polls show that neither party is held in high regard."

The latest court case came yesterday in San Diego when Rep. Randy "Duke" Cunningham (R-Calif.) wept openly after pleading guilty to tax evasion and conspiracy. His plea bargain came less than a week after public relations executive Michael Scanlon coolly admitted his role in a conspiracy to try to bribe a congressman.

Members of Congress, lawyers and pollsters recognize that both events taken together could signal the start of a cyclical ritual in the nation's capital: the moment when lawmakers and outsiders are widely seen as getting too cozy with each other and face a public backlash -- and legal repercussions -- as a result.

"I've been in town for 30 years, and it seems that every 10 years or so there is an episode of this type," said Jan W. Baran, a Republican ethics lawyer at Wiley Rein & Fielding. "We clearly are at that period now."

"It's gotten to a level that it can't be ignored anymore," agreed Stanley M. Brand, a criminal defense lawyer at Brand & Frulla who used to work for Democrats in Congress.

The worst of the blowback, both legal and electoral, could be blunted if ongoing probes turn up little or nothing. Indeed, some of the investigations are in the early stages and may take months or years to resolve. In addition, experts say that the most prominent cases are aberrational or else there would be even more investigations and indictments than there are.

Yet the activities under scrutiny can also be viewed as logical extensions of actions that once were rare but over time have become commonplace: massive political fundraising, freewheeling private travel given to lawmakers by groups interested in legislation, and the bestowing of other gifts and benefits on government officials by lobbyists.

As the Scanlon case demonstrates, the extent of this favor-buying has gone so far that the Justice Department is no longer deterred from bringing charges even if the gifts fall within Congress's gift-giving limits or are below campaign finance maximums. "It doesn't matter," Brand said. Charges could come, he said, if "anything of value is given to a public official that can be linked to an official act."

Scanlon was a partner of lobbyist Jack Abramoff, and they are under investigation for allegedly improperly extracting $82 million from Indian tribes. Scanlon has agreed to return $19 million and is cooperating with authorities, who have broadened their inquiries to include at least half a dozen lawmakers, some lawmakers' spouses and several aides-turned-lobbyists, lawyers involved in the case have said.

Prosecutors have told one lawmaker, Rep. Robert W. Ney (R-Ohio), and his former chief of staff that they are preparing a possible bribery case against them, The Washington Post has reported. About 40 investigators and prosecutors are also looking into the activities of several lawmakers, including Sen. Conrad Burns (R-Mont.), Rep. John T. Doolittle (R-Calif.) and former House majority leader Tom DeLay (R), who is facing unrelated campaign finance charges in his home state of Texas. Burns, Doolittle and DeLay have denied any wrongdoing.

The Post has also reported that investigators are gathering information about Abramoff's hiring of several congressional spouses, including DeLay's wife, Christine, who worked from 1998 to 2002 with a lobbying firm run by former DeLay staffers, and Doolittle's wife, Julie, who owned a consulting firm that was hired by Abramoff and his former law firm, Greenberg Traurig, to do fundraising for a charity he founded.

Separately, Senate Majority Leader Bill Frist (R-Tenn.) has been subpoenaed in connection with probes by the Securities and Exchange Commission and the Justice Department into his sale of millions of dollars' worth of stock in HCA Inc., the Nashville-based hospital chain founded by his father and brother. In yet another case, Rep. William J. Jefferson (D-La.) is under investigation by the Justice Department for possible violations connected with a telecommunications deal he was trying to arrange in Nigeria. Both lawmakers say they did nothing wrong.

At least partly because of public reports of these inquiries, voters' feelings about Congress have turned upside down since the start of 2001. In January 2001, 59 percent of Americans approved of the way Congress was doing its job and 34 percent disapproved, according a Washington Post-ABC survey. Earlier this month, the same poll showed that 37 percent approved and 59 percent disapproved.

In addition, for the first time in its 15-year history, the Wall Street Journal-NBC poll this year showed that the public's negative feelings exceeded its positive feelings about both political parties at the same time. "These are cautionary notes that are affecting both parties' political standing," McInturff said.