KEEP IN MIND that political contributions such as those listed below are perfectly legal and are the most effective means of financing expensive congressional campaigns. Small contributions from the folks back home are nice, but increasingly candidates rely on large, nationally based political action committees for the bulk of their campaign funds.

In 1979-80, the four political action committees that gave the most money to candidates for federal office were sponsored by the National Association of Realtors, the United Auto Workers, the American Medical Association and the National Automobile Dealers Association.

Last week, the House passed a bill to subsidize mortgages on new homes to the tune of $1 billion this year. The Senate Banking Committee has reported a similar bill that would grant $5 billion in subsidies over the next five years. This bill is a favorite of the home builders, but the entire industry--including the realtors--will benefit if it is enacted. The realtors' PAC contributed $1,536,573 during the last campaign.

In December 1979, Congress guaranteed $1.5 billion in loans to the Chrysler Corporation, saving that company from bankruptcy, at least for the time being, and preserving hundreds of thousands of jobs. the United Auto Workers' PAC contributed $1,422,731 to candidates in 1979-80.

Recently, the Senate Commerce Committee reported a bill that would prohibit regulation of the professions by the Federal Trade Commission. The American Medical Association's PAC gave $1,348,985 to candidates in the last congressional election.

The Senate Commerce Committee adopted yesterday, and its House counterpart is considering, a resolution that would nullify a proposed FTC regulation requiring used-car dealers to disclose known defects to buyers. The National Automobile Dealers Association PAC contributed $1,035,276 to federal office-seekers in 1979-80.

Congressional votes are influenced by numerous factors, including the interests of diverse constituencies and the objective merits of the proposal at hand. Not every supporter of the bills cited received PAC contributions. But to an increasing extent, large sums of money are being contributed to political campaigns by special-interest groups, and it is hard to believe the practice is not having an impact on the legislative process as well.