Spending for this year's congressional campaigns has reached new heights, with an increasing proportion of contributions coming from political action committees, the Federal Election Commission reported yesterday.

Incumbents were attracting almost three times as much cash as their challengers. Democrats candidates, meanwhile, not only outnumbered their Republican counterparts but also had raised more money by the mid-year mark, the FEC study said.

The biggest money-raiser and spender was Sen. Jesse Helms (R-N.C.). In second place, lagging $4 million behind Helms in each category, was West Virginia Gov. John D. Rockefeller IV (D), who is seeking a Senate seat.

The FEC study, which covered the 18 months from Jan. 1, 1983, through June 30, 1984, found that 2,019 candidates for House and Senate seats had raised $213.4 million, an increase of 21 percent over congressional fund-raising in the comparable 1981-82 period. Spending by congressional candidates totaled a record $161.8 million, also a 21 percent increase over the 1981-82 period.

Contributions to congressional candidates from political action committees (PACs) increased much more sharply, up 46 percent to $50.7 million from mid-year in 1982. The total also represents a 143 percent increase in PAC money for House and Senate campaigns since the last presidential election cycle in 1979-80, the FEC reported.

Contributions from individuals remain the largest source of funds for congressional candidates, but PACs are growing in importance, especially in the House, the study showed. PAC contributions accounted for 23 percent of congressional money raised by last June 30: 16 percent of the funds raised by Senate candidates and 30 percent of those raised by House contestants.

By contrast, at mid-year in 1982, PAC funds accounted for 19 percent of campaign cash: 12 percent of the Senate candidates' receipts and 24 percent for House candidates.

House and Senate candidates personally contributed 2 percent, or $4 million, of the money their campaigns had raised as of June 30. Political party contributions account for less than 2 percent.

The biggest money-raiser and spender on the House side in the 1983-84 cycle was Rep. Phil Gramm (R-Tex.), who collected $978,091 for a special election in February 1983. He spent $842,927 on that race and is now running for the Senate, ranking No. 6 as a senatorial money-raiser (with $3.7 million at mid-year) and No. 5 as a senatorial spender ($3.66 million by June 30).

An updated report, covering Gramm's finances through Sept. 30, shows that he has been spending money faster than he has been taking it in this year, having collected $5.4 million in contributions since Jan. 1 and paid out $6.5 million.

The FEC report showed that the 447 incumbents seeking reelection had received $118 million by mid-year while 1,229 challengers were able to collect $41.8 million. There were 343 candidates for open seats, and they had managed to raise $53 million.

By party affiliation, the roster included 1,031 Democrats who raised $115 million; 747 Republicans who got $97.6 million and 241 "others" who received $415,000. Senate Fund-Raising

The top Senate money-raisers were Helms, $9 million through June 30; Rockefeller, $5.33 million; North Carolina Gov. James B. Hunt Jr. (D), who is running against Helms, $5.31 million; Sen. Rudy Boschwitz (R-Minn.), $4.4 million, and Rep. Kent R. Hance (D-Tex.), who was defeated in his bid for the Texas Democratic senatorial nomination, $4.3 million. The candidate who defeated Hance, state Sen. Lloyd Doggett, ranked seventh on the mid-year list with $3.2 million in contributions. Senate Spending

The top spenders among Senate candidates were Helms, $8.8 million; Rockefeller, $4.9 million; Hance, $4.3 million; Hunt, $3.9 million, and Gramm. Boschwitz apparently had collected much more than he needed and slipped into seventh place as a spender, having paid out $2.9 million of the $4.4 million he raised by June 30. The sixth highest in expenditures was Doggett, with $3 million. House Fund-Raising

On the House side, the top money raisers behind Gramm were House Budget Committee Chairman James R. Jones (D-Okla.), $917,524; Rep. Stephen J. Solarz (D-N.Y.), $678,336; Rep. Joseph P. Addabbo (D-N.Y.), $675,465, and Manhattan Borough Democratic President Andrew Stein, the only challenger in the top five, $612,537. House Spending

The top spenders among House candidates, again behind Gramm, were Addabbo, $518,074; Rep. Charles Wilson (D-Tex.), $508,102; Pulaski County (Ark.) Democratic Sheriff Tommy F. Robinson, $487,942, and Arkansas Democratic Secretary of State Paul Franklin Riviere, who lost to Robinson in a runoff primary, $475,240. Political Action Committees ----

The largest amounts of PAC money went to incumbents. The top five recipients of PAC money in Senate races at mid-year were Boschwitz, $624,874; Sen. Howell T. Heflin (D-Ala.), $594,550; Sen. Walter D. Huddleston (D-Ky.), $543,694; Sen. Pete V. Domenici (R-N.M.), $533,795, and Sen. Charles H. Percy (R-Ill.), $522,654.

In House races, House Budget Chairman Jones led the PAC list with $362,943 in contributions. Following him were Gramm, with $263,125 (for the 1983 special election); House Minority Leader Robert H. Michel (R-Ill.), $248,992; Addabbo, $238,018, and Wilson, $220,550.