The nation's 3,479 political action committees are giving more money than ever to candidates for Congress, tilted heavily toward incumbents, according to a report released today by the Federal Election Commission.

The report shows that between Jan. 1, 1981, and June 30, 1982, the PACs gave $34.6 million to 1982 candidates for the Senate and House, more than 50 percent more than they contributed during the equivalent period for 1979 and 1980.

Of the $34.6 million, $27.5 million went to incumbents, $3.6 million to challengers and $3.6 million to candidates for open seats.

That is a ratio of more than 7 to 1 for incumbents over challengers. For all the 1979-80 election cycle, the incumbent-challenger ratio for PAC contributions was just over 2 to 1.

But the disparity is probably overstated, PAC analysts said, because incumbents are generally the first to be funded during a congressional campaign, while money for challengers comes at the end.

"I imagine that in July, August and September, a lot of money has started to flow to challengers," said Neil Newhouse, director of political affairs for the public affairs department of the U.S. Chamber of Commerce. "It's going to even up some, but I don't think it'll be like 1980."

That year was considered a breakthrough. For the first time, corporate and trade association PACs began to invest heavily in challengers, on the theory that the way to get a better result out of Congress was to change it. Previously, their contributions had been aimed at protecting their relationships with incumbents, whatever their ideology.

Newhouse said that the reversion to an earlier pattern of heavy incumbent giving "is an aberration . . . . What it reflects is that there just aren't as many viable challengers this year as there were in 1980."

The 18-month report also shows that Democratic candidates received $20.1 million from the PACs, to $14.5 million for Republicans. Labor PACs favored Democrats over Republicans $7.6 million to $600,000; corporate PACs favored Republicans over Democrats, $7 million to $5.4 million; and trade association PACs, which are dominated by business and professional groups, favored Republicans over Democrats, $5.1 million to $4.8 million.

The report showed that the most dramatic increase in money raised by PACs was by those with an ideological base. They raised $42.4 million in the first 18 months of the current cycle, triple the amount for the same period in 1979-80.

However, most of their money is spent raising money, pushing issues and making independent expenditures either to help elect or defeat a candidate, generally in television advertising.

The top five money raisers among all PACs in the reporting period were the National Congressional Club, $7.7 million; the National Conservative Political Action Committee, $7.2 million; the Realtors Political Action Committee, $2.2 million; the American Medical Political Action Committee, $2.2 million; and the Citizens for the Republic, $1.9 million.

The top five contributors to candidates in the reporting period were the American Medical Political Action Committee, $857,461; Realtors Political Action Committee, $614,110; UAW-V-CAP (United Auto Workers) $566,415; Machinists Non-Partisan Political League, $560,048; and the American Bankers Association BANKPAC, $471,515.