Some old issues in new dress, from the Clinch River breeder reactor to American troop levels in Europe, face Congress today as it rushes to approve stopgap funding for the government before leaving town this weekend for a month of campaigning.

With Congress due to return for a lame-duck session after the Nov. 2 elections, probably on Nov. 29, there is little pressure to act on anything more than a few appropriations bills and a "continuing resolution" to provide interim financing for the rest of the government.

But foes of the Clinch River reactor, which as it produced power would also produce plutonium that opponents warn could be used in nuclear weapons, are seeking to amend the continuing resolution to include language that would scuttle the long-controversial Tennessee project.

It took some heavy arm-twisting last year by Senate Majority Leader Howard H. Baker Jr. (R-Tenn.), the project's leading champion, to keep it alive. Even then, it survived in the Senate only by a vote of 48 to 46. With the courts having recently cleared the way for site work on the project, foes are pressing for a vote as quickly as possible and hoping that campaign sensitivities over the project's cost, now officially estimated at $3.6 billion, will help their cause.

Both sides said they expect the Clinch vote to be close. There is also opposition to the reactor in the House, but its opponents were blocked from forcing the issue there when the House version of the continuing resolution was considered without any opportunity for amendments.

Another possible domestic spending squabble arises over the Senate Appropriations Committee's decision, also as part of the continuing resolution, to strip the Federal Trade Commission of authority over doctors, lawyers and other state-regulated professionals. Opponents of the move have indicated they will seek to reverse it on the Senate floor or in conference with the House.

On the troops issue, Sen. Ted Stevens (R-Alaska), chairman of the defense appropriations subcommittee, put the Senate on notice yesterday that at least some Pentagon officials were trying to torpedo an Appropriations Committee recommendation to reduce U.S. troop levels in Europe by 23,000.

"There may be a concerted effort. . . with the active assistance of the Pentagon to overturn that recommendation," warned Stevens, who said the Defense Department's opposition came as a surprise in light of compromises worked out earlier between defense officials and the committee.

As approved by the Appropriations Committee, the Senate version of the continuing resolution includes the troop reduction mandate, and Stevens said yesterday he will fight to retain it. The House version of the bill would simply continue current spending levels for the Pentagon, without any troop reductions.

The Senate is scheduled to take up its continuing resolution today, with action expected tonight or tomorrow. The House passed its bill last week. Both versions would expire in mid-to-late December. Differences over the expiration date and other matters are to be resolved in a conference later in the week. Because existing spending authority for the government expires with the end of the current fiscal year at midnight Thursday, the bill must be passed and signed into law by President Reagan by then to avoid a disruption in government activities.

The Senate, by voice vote and without debate, yesterday approved a $7.1 billion military construction appropriations bill, which is $1.1 billion short of Reagan's request and $99 million more than the House approved. The Senate plans to act on the agriculture money bill today. These two bills, along with a housing funding bill, are the only appropriations that are believed to have a chance of enactment before Congress quits for the elections.