For Rep. John M. Murphy, one of the eight members of Congress implicated in the FBI's Abscam "sting" operation, being investigated is nothing new.

In fact, for Murphy -- who has proclaimed his innocence and says any FBI videotapes will exonerate him -- being investigated is one of the four major motifs of his congressional careeer. The others are fondness for foreign noncommunist dictators, a hatred for communism and aggressive retaliation when attacked.

All of these traits have been seen frequently during the 18-year incumbency that makes him the senior and most powerful Democratic member of the New York delegation.

Of Murphy's foreign friends, Murray Kempton wrote, "Murphy is more susceptible to the attractions of foreign tyrants than Oscar Wilde ever was to bellboys."

Shah Mohammad Reza Pahlavi, of Iran and General Anastasio Somoza of Nicaragua had close links to Murphy. People who traveled to Park Chung Hee's Korea and Murphy say he always received a hero's welcome there. Korean businessman Tongsun Park once gave him a legal campaign contribution.

Murphy began his congressional career after being another kind of hero in Korea -- a war hero who took a hill with hand grenades and his bayonet, winning the Distinguished Service Cross and the Bronze Star and also the Purple Heart for his wounds.

His only losing race was his 1960 first try for the seat he now holds.

He blamed the Liberal Party for siphoning votes from him and attacked them as "a parlor-pink minority group."

The cause of evil, Murphy has said in several situations, is communism.

The shah of Iran made Murphy a director of the Pahlavi Foundation of New York, which won a tax exemption, built a Fifth Avenue building and was a major element in the shah's American operations until his ouster a year ago.

Murphy served Somoza even more diretly. Last June, U.S. diplomats trying to persuade Somoza to step aside were astonished to find Murphy sitting on Somoza's side of the table.

When reporters asked if his last-ditch advice to his long-time friend Somoza was appropriate, Murphy replied belligerently that some U.S. members of Congress had gone to Hanoi. It was an odd comparison for a man to whom visiting Hanoi would be anathema.

About the same time, ABC-TV reporter Bill Stewart was murdered by Somoza guardsmen in Managua, "Steward shouldn't have been there," Murphy said in apparently trying to make the murder more justifiable.

Then he went further. "What did you really see?" he challenged the Staten Island Register's Brian Haugh, "all you saw is what the camera showed you." Somoza was ousted in July.

An audience of 350 to 400 mostly enthusiastic Murphy supporters turned out this week to welcome him on his first appearance back in his Staten Island stronghold since Abscam was revealed.

Men reached out to him. Women kissed his hand and he was given a standing ovation when he entered Prall Junior High School.

He drew only friendly laughter when the subject of videotapes came up. Asked whether the videotapes would show anyone taking a briefcase containing bribe money, he got laughs when he replied: "Well, that's why I want to see the videotapes."

Murphy drew cheers when he followed his pattern of counter attacking those who investigate him.

"He's a gunfighter. He doesn't back away at all," one admirer said.

Murphy demanded that Thomas Puccio, who heads the Justice Department's Organized Crime Strike Force in the Eastern District of New York, be removed from the Abscam case and said he has hired investigators to discover how information about him leaked to the press.

Before Abscam, Murphy was the subject of investigations by the Justice Department, the Securities and Exchange Commission and the Internal Revenue Service, all of them launched after his financial fortunes underwent a dramatic change in 1975.

Newsday has tracked Murphy's finances and reported that he was transformed rapidly from a man with large outstanding loans to a position of apparent financial security. "That financial comeback . . . cannot be explained by his congressional salary or other reported income," Newsday said.

An important, but not well-understood, element in Murphy's financial situation is a privately held company called American Chemosol Corp. of New York. Murphy lists his stock in the corporation, of which he has been board chairman, as worth more than $100,000.

Outsiders wonder how the stock can have any value since the company's activities and assets are not known. The firm was once working on a way to cut the nicotine and tar content of cigarettes.

The political gossip on Staten Island is that Abscam is unlikely to cost the 53-year-old congressman his seat unless he is charged and brought to trial. The local Democratic establishment turned out for his rally Wednesday although other candidates have said they will challenge Murphy in a primary.

Service to his constituents in the strange congressional district, which includes conservative, Catholic Staten Island and the lower East Side, Chinatown, Little Italy, and western Greenwich Village plus the lower West Side of Manhattan, has been a Murphy hallmark.

Even his political enemies concede he has been very good at helping constituents with problems ranging from getting potholes filled to dealing with the federal bureaucracy. One of the skills for which he was well known was helping people with immigration problems.

Murphy also has proved adroit at winning elections, even though his district boundaries have been changed five times and a lesser politician could find the present makeup of the 17th District impossible to handle.

In 1972, 74 percent of Murphy's Staten Island constituents voted for President Nixon while 62 percent of his Manhattan constituents voted for George McGovern, Murphy won easily in both places. As a conservative Democrat who was the only member of the New York delegation to vote against containment of hospital costs and voted for decontrol of home heating oil, he makes his odd district work well for him.

A conservative Republican doesn't stand a chance in the Manhattan portion of the district, so Murphy can concentrate on his Staten Island roots after disposing of whatever Democratic primary challengers he has drawn.