WASHINGTON (AP) _ The next congressional elections are still 18 months away, but the death knell already is being sounded on Capitol Hill for legislation designed to limit the role of political action committees in campaign financing.

''It does not seem likely that anything major will get through this session,'' says Elaine Milliken, counsel of elections for the Senate Rules and Administration Committee.

''It's likely there won't be anything this year,'' agrees Kathy Jarvis, staff director of the House Administration elections subcommittee.

The conventional wisdom on Capitol Hill is that election finance reform must be attacked very early in a two-year session - after members are finished with one campaign, but haven't started serious fund-raising for the next.

Bills have been introduced this year on both sides of the Capitol. However, they arrived without fanfare, and neither Senate Rules and Administration nor the House elections subcommittee has scheduled hearings.

''Legislation will not be passed in the next two years,'' said Jay Angoff, staff counsel for Congress Watch and a supporter of campaign finance reform. ''People are already getting into serious fund-raising for an election that's a year and one-half away.''

Randy Huwa, a lobbyist for Common Cause, agreed that campaign finance reform remains an ''uphill'' fight.

Political action committees run by business, labor and ideological groups contributed a record $104.9 million to congressional races in the 1984 elections, the Federal Election Commission reported.

This is up from PAC contributions of $83.6 million in the 1981-82 campaign period, $55.2 million in 1979-80 and $34.1 million in 1977-78, the FEC said.

A study by Common Cause, a self-described citizens' lobby, said House members seeking re-election last year got almost 80 percent of the $75.6 million PACs contributed to all House candidates, picking up $4.58 for every $1 given to challengers.

In the Senate, incumbents got $2.97 for each $1 going to opponents and collected about 65 percent of the $29.3 million PACs spent on the 33 Senate races last year, according to Common Cause.

The organization, which advocates changes in election finance law, said PACs last year accounted for nearly 30 percent of all campaign money. This is up from 24 percent in 1982, Common Cause said.

On Wednesday, the FEC reported that candidates spent a record $374 million on last year's congressional races, up 9.3 percent over the 1982 elections.

Although many politicians insist PAC money does not influence votes, Rep. Dan Glickman, D-Kan., told the elections subcommittee in 1982 about a conversation he once had with a colleague before the House voted on whether to regulate the used-car industry.

Glickman, who favors reform, recalled: ''A member commented to me, 'I committed. I got a $10,000 check from the National Automobile Dealers Association. I can't change my vote now.'''

Federal law says that a PAC can give a candidate up to $5,000 for a primary and the same amount for a general election. Individuals are limited to $1,000 for a primary or general election.

''The subcommittee will return to the subject someday. We're saying late this year at the earliest,'' said Ms. Jarvis. The chairman of Ms. Jarvis' subcommittee, Rep. Al Swift, D-Wash., favors public financing of congressional campaigns coupled with spending limits.

''We do not have definite hearing dates,'' said Ms. Milliken. But she said the panel's chairman, Sen. Charles McC. Mathias, R-Md., wants to hold them ''to get something on the record.''

''Mr. Mathias has said in the past that if there were support in committee to get a bill out, he'd get it out tomorrow,'' she said. ''There's little consensus in committee that I can discern at this point. It's going to be tough.''

Angoff of Congress Watch said many reformers believe congressional campaign financing will not be radically changed in the absence of another scandal similar to Watergate, which prompted public financing of presidential elections.

''I don't agree that a big scandal is necessary,'' he said. ''Eventually Congress will get so fed up they will voluntarily bite the hand that feeds them. But a big scandal would help things along.''

Common Cause's Huwa also said that changing the system will be an evolutionary process.

''A number of members of Congress would like to get off the treadmill,'' he said. ''There are people who are willing to change the system. More and more are uncomfortable with the system.''

''What will determine the outcome is enough dissatisfaction by the American public and members of Congress,'' Huwa said.