Sen. Daniel K. Inouye (D-Hawaii) opened a Pandora's box last month by the way he defended the five senators accused of improperly helping savings and loan executive Charles H. Keating Jr. "All of us," Inouye said, have intervened with regulators on behalf of campaign contributors.

Was Inouye right? Does everybody do it?

No, not according to several senators and top aides in more than 20 Senate offices. As might be expected, those interviewed said they would shy away from pressuring federal regulators on behalf of a major contributor like Keating. That was over the line, many felt, although there were many opinions of where the line began or ended.

Michael Lewan, chief assistant to Sen. Joseph I. Lieberman (D-Conn.), said he subscribes to "the mother rule." That means "if you can't explain something forthrightly to your mother, you shouldn't do it."

Everyone agrees that members should help constituents with bureaucratic snafus involving Social Security checks or Veteran's Administration benefits or Medicaid reimbursements, as congressional offices do thousands of times each year.

No one finds anything wrong with writing a letter that merely asks a federal agency to resolve a problem "as quickly as possible within applicable rules and regulations" -- words that some members use to protect themselves against accusations of improper influence.

It is less common -- but not unusual -- for a member or top aide to call a regulator about a generic problem that affects many constituents, such as farmers or small businessmen.

But after that the line becomes fuzzy -- particularly when it comes to helping a single business or a powerful campaign contributor. Sen. John C. Danforth (R-Mo.) noted that he has received donations from McDonnell Douglas aerospace employees and responds when the firm has problems, because it is the biggest employer in his state. "It may just be best to rely on disclosure and let the people decide," he said.

Sen. Paul Simon (D-Ill.) was embarrassed last year when his top aide wrote a letter to a federal student loan guarantee agency official asking that he reduce the repayment schedule of a cooking school owner who was raising money for the senator.

Simon refunded the money, called the incident an aberration and told his staff to keep fund-raising separate from constituent service.Are Conflicts of Interest Inevitable?

Such conflicts of interests may be inevitable in today's American political system. Running for Congress requires a lot of money, after all; people who can raise large sums usually are interested in establishing a relationship that lasts beyond Election Day. Keating said explicitly that he hoped his fund-raising skills would buy him influence.

There are countless examples like Simon's intervention for a fund-raiser. But none compare to the Keating case. It stands alone because of the amount of money involved and the fact that the political overtones of Lincoln's $2 billion failure have made it a metaphor for the savings and loan debacle.

To avoid such conflicts, some senators said they have developed their own guidelines about how and when they will intervene. (The Senate has no specific written standard on handling interventions, a major point of contention in the Keating case.) Howell T. Heflin (D-Ala.), chairman of the Senate Select Committee on Ethics that must judge the conduct of the "Keating Five," said, "We don't do a lot of advocacy." His general rule is to limit his staff to asking an agency to meet with a constituent who has a complaint.Contributors Who Face 'Confrontation'

Sen. Warren B. Rudman (R-N.H.), vice chairman of the committee, said he has an additional rule. He avoids accepting substantial contributions from any company during a period in which the company is facing a "major confrontation" with regulatory agencies.

A major confrontation is what Keating faced in 1987. Federal regulators were threatening to shut down his Lincoln Savings and Loan; Keating sought help in keeping the regulators at bay. Sens. Alan Cranston (D-Calif.), Dennis DeConcini (D-Ariz.), John Glenn (D-Ohio) John McCain (R-Ariz.) and Donald W. Riegle Jr. (D-Mich.) have insisted that their actions on Keating's behalf were not triggered by the $1.3 million he raised for their campaigns and causes.

Sen. Jesse Helms (R-N.C.), a member of the ethics committee, says he thinks the public believes Keating was buying influence. And he told Riegle last week he doubts any of the accused senators would have gotten involved with Keating -- whom he called "Daddy Warbucks" -- if the thrift operator hadn't been "giving away other peoples' money."

Sen. Ernest F. Hollings (D-S.C.) places blame elsewhere. He said in an affidavit attesting to the integrity of the five colleagues that "King Solomon would have difficulty separating constituent contributions from a senator's expected constituent service." It is the current political campaign financing system that is "corrupt," he said. "There is too darn much money required to seek and hold office."

Sen. Jake Garn (R-Utah) said in another affidavit in the case that he didn't know the facts of the Keating affair well enough to "pass judgment" on his five colleagues' conduct.

But he added that he never intervened with regulators for a single financial institution while he was chairman of the Senate Banking Committee. "I would not consider it appropriate for me to engage in such conduct," he said.

Garn said he has helped individual farmers battling federal land management agencies over wetlands regulations. He argued against making specific regulations governing conduct on intervention, however.

"I don't think I can give you a set rule," he said. "If I did it would limit my effectiveness. You can find one individual with a just case."

When Inouye testified in December, he said he

had once asked an agency to overturn a regulation. But he said that was in the 1960s and it affected the entire sugar industry, an important part of his state's economy.

Patrick H. DeLeon, Inouye's top aide, said it is "very, very rare" for Inouye to call a regulator or ask for a meeting for a constituent. "He much prefers a letter . . . to be very clear." And the letter, DeLeon said, always contains a phrase asking the agency to consider the case "within applicable rules and regulations."

Susan Magill, top aide to Sen. John W. Warner (R-Va.), agreed. "Our policy is to try to give constituents a level playing field 'consistent with federal law and regulations.' . . . It would be extremely rare for Senator Warner to call or write an agency and say, 'This is what I think you should do.' "Most Constituents Aren't Like Keating

Roy M. Neel, who runs Sen. Albert Gore Jr.'s (D-Tenn.) office, said, "At first blush, I guess you can say 'Everybody does do it.' " But most constituent requests are much different than Keating's, he said. They usually divide into those seeking help with bureaucratic paperwork and those with some legal problem.

He recalled that the entire Tennessee congressional delegation attempted to help financially troubled Fisk University in Nashville, a predominantly black college.

But Neel added, "When it's a private concern you have to stop and ask questions, whether it's a major employer or not. Do they have a legitimate gripe? You never hesitate to ask any official of the federal government the status of a case and say you hope the constituent gets a fair hearing." In contrast, he said, "intervening in something in the courts is sort of no man's land. Most offices wouldn't touch that case."Battling the Red Tape With Gusto

Samuel Poole, administrative aide to Sen. Terry Sanford (D-N.C.) said, "The senator and I believe, quite frankly, in intervening aggressively to cut some of the bureaucratic red tape."

He cited a case in which the office helped a constituent who "probably was a contributor" get approval to do some business in Cuba.

Niels C. Holch, top aide to Sen. Mitch McConnell (R-Ky.), said if he knows someone seeking help is also a contributor "we analyze the request as if money wasn't a factor. Would we be helping if the person wasn't a contributor? That decides the course of action. We take cases on their merits."

Holch said McConnell's office has responded to 22,000 constituent cases in his first term. The senator got involved personally in fewer than 10, he said. One was to help a sailor get extra leave to visit an ailing grandmother, another to get a visa extended for a foreign doctor at a university medical school.

During last week's hearings, Helms challenged Cranston's claim -- illustrated as the hearings started with charts naming each colleague's "designated staff fund-raisers" -- that members can't separate fund-raising and legislative activities.

Helms and aides to several other senators said that most "designated staff fund-raisers" don't raise money at all. They serve only an administrative function of redirecting contributions from the Senate office to the campaign headquarters.

R. William Johnstone, chief of staff for Sen. Wyche Fowler Jr. (D-Ga.), said he isn't even listed as a designee, "mostly for appearances."

Holch was one of the few "designated fund-raisers" who acknowledged he did help in fund-raising. He said he sometimes has asked supporters to sponsor fund-raising events for the senator.

Lieberman aide Lewan said the Keating hearings have had "a profound effect on staff people here. You sit and watch people just like yourself and what they did and didn't do and write and didn't write. It has really scared people."

He said he asked an ethics expert to brief the staff recently after some aides inquired whether standards were changing. "No one would have asked me that a year ago," Lewan said. Staff researcher Lucy Shackelford contributed to this report.