The 100th Congress plans to adjourn this week once it clears its desk of unfinished business, including a campaign-year attack in the war on drugs.

The fate of dozens of bills lies in the balance as the House and Senate begin what both sides agree will be the last week of the two-year Congress. The biggest of the bills is a massive anti-drug package passed by the Senate last Friday.The Senate bill isn't as tough on drug users as one passed earlier by the House, and negotiators from both bodies will be meeting to try to resolve the differences. If they agree on a single package, a final vote will be needed in the House and in the Senate before it can go to President Reagan.

House and Senate negotiators were bogged down on another major legislative package - so-called technical corrections to a 1986 tax bill. In addition to making technical corrections, the proposal included selected new tax reductions, the tax increases to pay for them, and a "bill of rights" for taxpayers facing enforcement or collection from the Internal Revenue Service.

Differences in the House and Senate versions of the bill were so sharp that negotiations broke down Friday, and an aide to House negotiators said "whether the conference gets back together at all again is very much up in the air."

On the other end of the priority list were bills ranging from legislation designed to assist individual people, nominations of federal judges, water projects affecting specific cities and states, and a plan to end the United States' trusteeship over the western Pacific island nation of Palau.

Yet another bill that could make it under the wire would elevate the Veterans Administration to Cabinet-level status.

Senate Majority Leader Robert Byrd told senators on Friday that "I certainly would hope we wouldn't have to stay beyond Wednesday. But nobody can predict that."

The House returns from a long weekend on Tuesday with a scheduled vote on legislation that would require full disclosure of credit card information to consumers.

The bill, passed by the Senate last week, requires that banks, department stores and other companies that offer credit cards tell consumers about annual fees, interest rates, late fees and other information.

Also pending is legislation providing first-ever restrictions on lobbying by former members of Congress, part of a general tightening of federal rules against influence peddling by top government officials.

The legislation has passed both houses of Congress in different versions, and a compromise will have to be worked out before it can be sent to Reagan.