Election-year Congress acts on more-popular bills.

As Congress breaks for the Republican National Convention, election-year pressures are reaching a peak on Capitol Hill. With only four weeks left on the legislative calendar after Labor Day, both parties are positioning themselves on issues before Election Day.

As a result, the lawmakers continue to leave some unpopular issues untouched, while moving on toxic waste and completing a bill to give religious groups access to school facilities. Democrats continued to hammer at Reagan policies in Central America, but granted the President much of the money he asked for El Salvador.

''It's been pretty much like we had predicted - that politics would reign supreme,'' said House minority leader Robert H. Michel (R) of Illinois in an interview just before the recess. He ticked off issues left unresolved, from natural-gas deregulation to an overdue rewrite of the Clean Air Act to criminal-law reform.

The one exception to the politicking was the immigration reform debate, said Representative Michel, calling it the ''best'' and least partisan of the session. But the mood has changed since the debate, and most observers, including Michel, consider the immigration bill dead for this session.

Some House Republicans have bitterly protested the domination by Democrats, especially by Speaker O'Neill. ''Some of us are concerned that the operation up there [in the House] has become extremely partisan, extremely political,'' Rep. Richard Cheney of Wyoming, chairman of the House Republican Policy Committee, told reporters last week. He put the blame on the shoulders of O'Neill, citing his sometimes harsh personal criticisms of the President.

''There's a lack of any sense of restraint,'' Representative Cheney protested.

The Speaker dismisses charges that Congress is more partisan than in previous election years, saying that such statements come from members who have only been on Capitol Hill for two or four years.

Minority leader Michel expressed little surprise about the election-year mood.

''It's frustrating for the Speaker, who sees the President being able to fare so well'' in the public eye, Michel said. ''That's been so frustrating for Tip - that someone he sees as a Hollywood actor can in this serious business of legislation have such a command over the flow of events.''

In fact, neither party has taken clear control of lawmaking in recent weeks. O'Neill has made his speaker's post into a platform for dispensing the Democratic viewpoint, the White House has kept a relatively low profile, except in key areas such as Central America, and the GOP Senate has steered an independent course, as members keep a watch on their own reelection campaigns.

In one clear sign of senatorial wariness, the upper chamber rebuked the President for appointing the controversial Anne Burford, former chief of the Environmental Protection Agency, to an advisory council. The GOP-led Senate beat even the House Democrats to the punch on that issue.

But there have been defeats, victories, and compromises for all the major participants on Capitol Hill in recent weeks.

Among the top issues:

Central America. The Reagan administration has failed to persuade Congress to vote more money for covert operations opposing the leftist government of Nicaragua. But neither would the House go along with O'Neill, who declared he was ''frightened'' by the military buildup in the region and wanted to deny any more funds this year.

The lawmakers moved to the safe middle ground by granting $70 million more for military aid to El Salvador, where the recently elected government is fighting leftist guerrillas.

Toxic waste cleanup. Nearly every area of the country has some hazardous waste site, and the House moved last week to raise $10.2 billion from 1986 to 1990 to clean up an estimated 546 of these dumps. Despite the high cost, the legislation has such broad interest that final passage by both houses of some increase in the Superfund for toxic cleanup can be expected, especially with elections so close.

Religion and schools. Although Congress has denied school prayer supporters a constitutional amendment, it has given them a consolation prize in the form of the ''equal access'' law. The measure allows student religious groups to use school buildings after school hours, just as secular groups can use the facilities.

Defense spending. House and Senate leaders appear hung up indefinitely on the gigantic defense authorization bill for 1985, with the White House holding out for $299 billion and the Democratic House standing pat on a position for a few billion dollars less. The two sides will have only the few weeks after Labor Day and before adjournment in early October to resolve the dispute.