Congress returned yesterday from its second midsummer break for political conventions and will settle in for seven weeks of work before taking off Oct. 4 for election campaigning. Party leaders had hoped to quit for the year then, but House Speaker Thomas P. (Tip) O'Neill Jr. said yesterday he "can't conceive" of the House being able to finish its work that soon. That would bring Congress back Nov. 12 for the first post-election session in a presidential election year since 1948, when Harry S Truman pulled his famous upset to hold onto the White House.

The main hangup is the need to pass a second budget resolution setting a binding spending ceiling which is always terribly difficult in the House, where the budget proces has always been a very partisan issue. O'Neill fears it would be impossible to pass the resolution in an election atmosphere.

In addition to the budget resolution, Congress also must approve 13 appropriation bills, none of which has yet passed the Senate, and legislation extending authorization for a host of existing programs -- such as aid to higher education, mass transit, airport development, and housing and community development -- all of which are expected to eventually pass because federal money has been flowing into these areas and they have developed powerful constituencies.

Then Congresss will try to break some new ground. Bills to protect more than 100 million wild acres in Alaska and to put enforcement teeth in the law forbidding racial descrimination in the sale and rental of housing seem almost certin to pass after years of struggle. Creation of a "super" fund" to clean up hazardous waste dumps such as Love Canal and a bill to help build slurry pipelines to move coal long distances cheaper than by rail are also on O'Neill's list of priority bills.

Missing from that list is the monumental bill to revise, update and make uniform the federal criminal code. For the first time, a bill has emerged from the House Judiciary Committee, but O'Neill says he has been told it would take three days on the House floor and he doesn't know where to find the time. But if the Senate passes its version of the measure, O'Neill said, he would try to make time for it. The Senate, which has passed the bill before, had been waiting for its chief sponsor, Sen. Edward M. Kennedy (D-Mass.) to return from the presidential campaign trail.