Breaking all previous election financing records, 100 political action committees collected $75 million to influence races for federal offices in 1979 and 1980, a Washington Post study shows.

Then, in a flurry of spending as the general election neared, the PACs deployed about $10 million in a mere three weeks, mostly in connection with House and Senate contests. That was 14 percent of the $73.3 million they had spent in nearly 23 months.

Reports filed with the Federal Election Commission show that the 100 PACs accounted for about 60 percent of all of the money raised and spent by the more than 1,700 non-party units that were active between Jan. 1, 1979, and Nov. 24, 1980. The grand total of receipts, $127.3 million, was $50 million more than in the same period of 1977-1978. Outlays increased by $46.3 million.

The top 100 PACs included 16 sponsored by trade associations that spent $10.2 million while those of 13 corporations spent $4.1 million, including nearly $800,000 by three defense contractors. The PACs of 33 union organizations spent $18.8 million. Ten health-related units paid out $6.2 million.

But all of the three top-ranking PACs were nonparty conservative or right-wing units. The three alone accounted for nearly one-quarter of the top 100's receipts and expenditures.Their combined income was $18 million, their outlays $16.8 million.

Ranking first was the National Conservative PAC, which raised and spent more than $7 million, including $1 million in the final three weeks before the Nov. 4 balloting. Then came the Congressional Club, which began as a fund-raising unit for Sen. Jesse Helms (R-N.C.). It spent $6.6 million, including nearly $1.5 million in the brief preelection period. Placing third, with outlays exceeding $3 million, was the Fund for a Conservative Majority.

Moreover, the 100 top PACs included eight other similar units that took in an additional $5.9 million and spent an additional $5.5 million, raising the conservative/right-wing shares to 32 percent of receipts and 30 percent of outlays.

Many candidates helped by these PACs were also heavily favored by pro-gun and antiabortion organizations, and, sometimes, by units sponsored by trade associations, health-related groups and corporations.

Two pro-gun PACs, ranking 11th and 18th, together raised $2.4 million ans spent $2.2 million. Their receipts were 14 times those of the PAC of Handgun Control Inc., which raised only $168,267 -- $40,733 less than was taken in by the 100th-ranking unit.

An antiabortion PAC, 34th on the list, spent nearly $600,000. But two proabortion units, ranking 52nd and 65th, together spent $77,000 more.

The PAC of the National Association of Realtors, which played a key role in the defeat of legislation to put enforcement teeth in the fair housing law, led the trade associations. Ranking ninth on the top 100 list, it accounted for better than one fourth of the associations' combined $10 million in income and outgo.

The pace-setter among the health-related PACs was AMPAC, sponsored by the American Medical Association. It came in 7th with outlays of $1.8 million. The units of seven AMA-affiliated state societies -- Texas, California, Florida, Pennsylvania, Illinois and Ohio -- increased the medical total to $4.8 million. The PACs of the American, California and New York State dental associations paid out a combined $1.2 million. The unit of the American Chiropractic Association spent $156,164.

Among the 13 corporate PACs that raised and spent a combined $4.1 million, the leader, with spending of $706,000, was the Chicago & Northwestern Railroad; it ranked 29th on the top 100 list. The three defense contractors: General Dynamics, which spent $353,660; Grumman, $305,370, and Vought, $130,758. Standard Oil of Indiana (Amoco) spent $360,313, the Winn-Dixie grocery chain, $249,311, and American Family Corp., $317,211. AFC is the leading seller of cancer insurance.

The 33 union PACs that took in and distributed about $19 million, or one-quarter of the spending total, were led by the United Automobile Workers unit. It took sixth place on the top 100 list with outlays of $2 million. Among the 33 were seven maritime PACs, which spent a combined $2.9 million; five transportation units, $2.6 million, and four education units, $2.4 million.

Four agricultural PACs, placing from 12th to 55th, spent $2.5 million. The unit of the Associated Milk Producers Inc. (AMPI), one of the three dairy cooperatives on the list, accounted for more than half of that sum. t

In all, the more than 1,700 active PACs included 403 trade/health units that spent $31 million; 905 corporate, $30.6 million; 201 union, $24.2 million; 153 non-connected or ideological, $32.4 million, and 28 dairy and other cooperatives, $2.6 million.

For the full 24-month cycle of the 1976 presidential election, according to FEC data, spending by the 450 corporate PACs then in existence totaled $5.8 million -- only $1.7 million more than was spent by 13 such units this time around. The 303 union PACs registered in 1976 spent $17.5 million, or $2.5 million less than 27 such units paid out in 1980. The FEC has compiled data on PAC receipts and outlays in the 1976 elections only for corporations and unions, for the 1976 races are complete only for corporations and unions.

Many candidates supported by organized labor were also aided by the nonpartisan, 10th-ranking National Committee for an Effective Congress, which spent $1,350,037; the Council for a Liveable World, $412,565, and the League of Conservation Voters, $446,375. The nonpartisan Women's Campaign Fund took 30th place by spending $689,312 for women candidates.

Mass fund-solicitation mailings to voters consumed large proportions of the outlays made by several nonpartisan PACs, particularly such conservative/right-wing units as NCPAC. And much of the money left over went for so-called "independent expenditures" in behalf of candidates who were required by the election law to give neither consent nor cooperation to such spending. Some independent outlays were "negative," i.e., made against opponents of the favored candidates.

Under a 1976 Supreme Court ruling, the First Amendment's guarantee of freedom of expression tolerates no restriction on independent expenditures for or against a candidate, even though, the court held, the Constitution allows the law's limits on direct contributions to a candidate.

The Congressional Club led in independent expenditures: $4,174,601, or 63 percent of its total outlays. NCPACs were $2,819,491, the Fund for a Conservative Majority's $1,744,616, and Christian Voice's $127,299. The total, $8,866,607, was 6.6 times their direct contributions.Included were substantial sums for President-elect Ronald Reagan.

By contrast, most PACs spent relatively little on fund-raising and little or nothing in independent expenditures (although this may change sharply in 1982); but they gave very large proportions of their receipts in direct contributions to candidates, mostly those who ran for the House and Senate.

The 10 leaders in direct contributions were the PACs sponsored by the Realtors, $1,564,905; UAW, $1,474,431; AMA, $1,258,222; National Automobile Dealers Association, $1,045,606; International Association of Machinists, $828,335; AMPI, $743,089; AFL-CIO, $718,052; The Seafarers International Union, $663,748; the Marine Engineers Beneficial Association (MEBA), $646,495 and American Dental Association, $645,725.

Following are PACs among the top 100 that were unnamed above. The dollar figure given is for either receipts or expenditures, whichever was higher. Receipts are denoted by an asterisk: NONPARTY

Conservative/right-wing: Citizens for the Republic, $2.3 million*; Committee for the Survival of a Free Congress, $1.6 million*; Conservative Victory Fund, $508,780*; Republican Senate Majority Fund, $427,590*; Americans for Constitutional Action, $244,429*; Inter-Mountain, $209,000*; Western Intermountain, $255,016*.

Guns: Gun Owners of America, $1,292,355; National Rifle Association, $1,036,381*.

Antiabortion: Life Amendment, $590,847*.

Proabortion: National Abortion Rights League, $407,918*; Voters for Choice, $333,277*.

Others: Veterans of Foreign Wars, $285,516*; American Tax Reduction, $220,613. TRADE ASSOCIATIONS

National Association of Life Underwriters, $959,543; American Bankers Association, $714,584*; National Association of Homebuilders, $535,175; Business Industry PAC, $546,061*; Association of Trial Lawyers of America, $536,629; National Rural Electrical Cooperative Association, $440,881; Independent Insurance Agents of America, $386,375; Louisiana Energy, $390,765; Associated General Contractors, $371,703*; Mercantile Exchange, Chicago, $340,325*; U.S. League-Savings Association, $342.824*; American Trucking Association, $285,503; National Federation of Independent Businesses, $218,682; National Tooling and Machining Association, $270,137*. CORPORATE

International Paper, $300,004*; General Motors, $241,898; Tenneco, $238,163*; Dart Industries, $259,439; General Electric, $249,135*; Fluor, $247,900. AGRICULTURAL

Dairymen Inc., $597,499*; Mid-America Dairymen, $493,826*; Alabama Farm Bureau, $383,295*. UNION

General: International Ladies Garment Workers, $1,221,957*; United Steelworkers, $993,495; United Food & Commercial Workers, $762,447*; Communications Workers of America, $677,620*; Carpenters and Joiners, $649,148; International Union of Operating Engineers (IUOE), $473,380*; Laborers' International Union, $457,152; the terminated Thomas Jefferson Fund, $337,204*; International Brotherhood of Electrical Workers, $259,174; District 1199, National Union of Hospital & Health Care Employes; Hotel and Restaurant Employes and Bartenders International Union, $214,007; Local 825 of IUOE, $245,284*.

Maritime: MEBA District 2, $473,361*; MEBA retirees, $430,644; Local, International Longshoremen's Association, $377,519*; Masters, Mates and Pilots, $280,852* from a PAC and $240,243 from a pensioners' unit.

Transportation: United Transportation Union, $1,190,141; Brotherhood of Railway, Airline and Steamship Clerks, $494,709*; Airline Pilots Association, $433,687; International Brotherhood of Teamsters (IBT), Ohio, $245,368; IBT, $240,541*.

Education: National Education Association, $956,263; American Federation of Teachers (AFT) VOTE COPE, $935,182; Minnesota Education Association, $253,684; AFT COPE, $282,761.

Public employes: American Federation of Government Employes, $582,736*; American Federation of State, County and Municipal Employes, $496,845*.