The Senate returned from its Thanksgiving recess yesterday to begin debating legislation that would limit campaign contributions that congressional candidates could accept from political action committees (PACs) but increase the amount that individuals could donate.

With only a handful of senators on the floor, Sen. David L. Boren (D-Okla.), the measure's chief sponsor, charged that the proliferation of PACs and their growing importance in financing congressional campaigns threatens to fragment the country's political system and overwhelm "grass-roots democracy."

"We cannot expect members of Congress to act in the national interest when election campaigns more and more are being financed by the special interests" as represented by the PACs, Boren said.

But opponents of the measure, led by Sen. John Heinz (R-Pa.), said the Boren proposal was flawed, would have unintended benefits for incumbents and should not be rushed through the Senate without thorough committee hearings. Heinz is chairman of the National Republican Senatorial Committee, which raises money for GOP Senate candidates.

"No legislative body, particularly the United States Senate, should legislate by spasm," Heinz said in urging the Senate to table the proposal.

He is expected to offer a motion to table the measure today, when the four hours set aside to debate the proposal expire.

Senate Majority Leader Robert J. Dole (R-Kan.) predicted yesterday that the effort to block passage will succeed.

Dole, like Heinz and other opponents, cited procedural objections to the Boren proposal. He said he supported changing the campaign financing system but did not want laws "written on the Senate floor" without prior hearings.

The Boren measure, which was offered as an amendment to nuclear-waste legislation now before the Senate, would limit the amount of campaign contributions House candidates could accept from PACs to a total of $100,000 in each election. The PAC contribution limit for Senate candidates would be between $175,000 and $750,000, depending on the size of the state.

The measure would also reduce the amount a PAC could contribute to a single candidate for federal office from $5,000 to $3,000 and would increase the amount individuals could contribute to a candidate from $1,000 to $1,500.

In an attempt to blunt the impact of negative advertising campaigns against candidates financed by some PACs, the measure would require broadcasters to provide equal time to candidates who are the targets of such a campaign.

The legislation would be effective beginning with the 1988 congressional elections.

Boren said that in the 1984 elections, 163 House and Senate candidates received more than half of their contributions from PACs. He said there are now more than 4,000 PACs and that their total contributions to congressional campaigns had skyrocketed from $8 million in 1972 to more than $113 million in 1984.

Brushing aside Heinz's plea for more time to consider overall campaign finance reform, Boren said, "How long are we going to wait? Are we going to wait like the drug addict until every member of the House and Senate is hooked on special-interest money?"

Heinz's opposition to the measure was supported by Sen. Charles McC. Mathias Jr. (R-Md.), an advocate of public financing of congressional campaigns.

Mathias said he feared the changes proposed by Boren would lead to more "fat-cat contributions" by wealthy individuals and would not "get to the real causes of the problem," which he said included the fact that congressional campaigns are "too long and too costly."