From 1971 through 1975, members of the Senate earned nearly $4.1 million in outside income from speaking engagements and articles.

Records compiled by The Washington Post and Congressional Quarterly show that many of the fees - often $1,000, $2,000 or even $500 for a single engagement, plus expenses in many cases - came from organizations with direct interest in legislation before Congress.

For 1975, for example, senators reported fees for speeches to such organizations as the Railway Clerks Union, American Meat Institute, Sheet Metal and Air Conditioning Contractors Association, Grocery Manufacturers Association, Association of Retail Druggist, American Bankers Association and many other unions and business groups.

It has been common talks on Capitol Hill for years that at least in some cases speaking invitations don't just represent a desire on the part of a trade group to listen to someone who really understands what's going on in the Capitol. Rather, there has been a strong suspicion that on occasion invitations represent an attempt by the trade group or union to curry goodwill with a senator and thereby develop a better "image" or "posture" with him for future legislative efforts.

That suspicion, basically, is the reason why both the House and the Senate, under pressure from constituents who believe a salary just raised to $57.50 a year ought to be enough, are clamping a limit of $8,625 a year on the amount a member can earn from outside speaking fees and articles. The lid is being imposed in a new code of ethics now on the Senate floor. The House has already adopted the ceiling.

Whatever the fairness or unfairness of the limit, many senators, like Gaylore Nelson (D-Wis.), chairman of the special committee that wrote the proposed Senate ethics code, Majority Leader Robert C. Byre (D-W. Va.), Abraham A. Bibicoff (D-Conn.) and Dick Clark (D-Iowa), believe the hugh lecture fee totals piled up by some senators create an inference of hanky-panky and lower the the Senate in Public esteem.

Clark, emphasizing the fact that it doesn't all come from university teas, read into the record figures showing that construction groups had paid about $84,000 in honoraria from 1972 to 1975, banking groups about $185,000 from 1972 to 1975, and labor groups about $100,000 over the same period.

Statistics based on honorarium reports, required to be filed by senators each year, show that senators received $787,000 in honoraria in 1971, $618,000 in 1972, $1,087,00 in 1973, $94,000 in 1974, and $638,00 in 1975. This totals $4.1 million over five years. Final totals on 1976 reports aren't available yet.

Over the years, Hubert H. Humphrey (D-Minn.) has been by far the biggest earner, totaling $233,00 for the five-year period 1971 through 1975. His fees have come from lots of university groups, lots of religious and charitable organizations holding fund-raising dinners, but also from lots of businesses and unions - the Railway Clerks, Chamber of Commerce, Young and Rubicam, the Retail Clerks, Univac, the car and truck rental and leasing associations and the like.

Another with a big total over several years has been Mark Hatfield (R-Ore.), with $132,000 from 1972 through 1976. Hatfield, a religious man, makes most of this money from speaking before Protestant religious groups. Another with high totals is Bob Dole (R-Kan.), who made $105,000 from 1972 through 1975, speaking to such organizations as the Machinery Dealers Association, Gypsum Dry wall Contractors, and the National Association of Home Builders.

In an angry debate that lasted over a week and is still dragging on, Sen. Edmund S. Muskie (D-Maine) made the argument that since the Senate wasn't imposing a limit on member's income from interest and dividends, it shouldn't limit his honoraria either. Nelson and others, arguing that collection of interest and dividends requires no active effort, while speaking takes a man away from the job and requires him to perform services, defeated a Muskie move to wipe out the $8-625 lid.

Humphrey voted to keep the lid. Conceding he had made some money on the speaking circuit than anyone else and that a house he owns in Minnesota is called "the home that wind built," he added, "but we are getting a salary of $57,500 a year. In my state that is a lot of money."