Sen. Russell B. Long (D-La.), chairman of the Senate Finance Committee, isn't doing too badly financially himself these days.

Already a millionair from his oil, gas and real estate holdings, Long had income from his petroleum-based portfolio of more than $420,000 last year.

Now he has turned his money-making talents toward stockpiling funds for his reelection bid this fall -- a race for which he does not yet have an opponent.

But he does have $461,000 in contributions, mostly from individuals associated with the industries affected by legislation he controls.

As chairman of the committee that has life-or-death power over tax legislation, and as a ranking member of the Commerce Committee, long has come through for his many friends in the business world. This year they are coming through for him. For example:

Oil and gas interests contributed more than $67,000. "That's our No. 1 economic interest" in Louisiana, Long said in an interview. "Louisiana has been moving up very nicely in per capita income [relative to other states] directly because of the increase in the price of oil and gas." Long helped raise the price by helping to take controls off the industry.

Insurance executives nationwide have contributed more than $20,000. Long helped the industry with a 1977 tax break, but attributes the support from insurance executives to his proindustry stance on national health insurance.

The maritime industry, an economic mainstay in Louisiana's river and gulf regions, has contributed nearly $30,000. It is asking Congress for antitrust exemptions and changes in the way federal shipbuilding subsidies are administered.

Rice growers and brokers have contributed $12,000 to Long, who said: "I have worked to try to find markets for rice, and when I've helped Louisiana rice, I've helped the whole industry." Most rice-related contributions are from outside Louisiana.

Even funeral directors, whose economic interest lies in trying to get Congress to pull the teeth of the Federal Trade Commission, have rallied to Long's support. He has received $1,800 from seven out-of-state funeral directors.

"I think that all business people ought to be politically active," Long said of the funeral directors' contributions. "They ought to take an interest in government, because it could be a matter of life or death to them."

Long's reelection campaign is anything but a life-or-death struggle. The 61-year-old senator has no opposition in his bid for a fifth term; he may be reelected by acclamation. Still, he raises funds at a fevered pitch.

Long's list of financial backers reads like Standard and Poor's directory of corporate executives.

It includes the chief executive officers of Tenneco Inc., IBM Corp, Rockwell International Corp., PPG Industries Inc., Bendix Corp., the Prudential Insurance Co. of America Inc., Connecticut General Life Insurance Co., Occidental Petroleum Corp., the Winn-Dixie Stores, Raytheon Inc., Addressograph-Multigraph Corp., General Telephone and Electronics Corp., General Electric Co., Exxon Corp., E. I. duPont de Nemours & Co., Hewlett-Packard Co., Cities Service Co., and Gulf Oil Corp.

Long now faces the problem of what to do with the money he has collected if no one runs against him. July 11 is the deadline for an opponent to file.

Under campaign reform laws that he helped to pass, Long has three choices if no opposition surfaces: He could keep the money for his next race, give it back to contributors, or pass it on to other candidates, subject to contribution limits. He cannot legally convert it to his personal use.