Barack Obama heads to Capitol Hill on Monday to confront mounting concerns about the size of his economic stimulus plan, but all eyes will be on the growing farce surrounding his vacant Senate seat that could lead to a physical showdown.

In an example of how the US Congress can mix transcendent questions of state with political circus, Mr Obama will meet party leaders the day before the man named as his Senate replacement risks being manhandled by armed police if he tries to enter the chamber.

Roland Burris, an African-American, has been named by Rod Blagojevich, the Illinois Governor facing corruption charges, to fill the seat. Mr Burris, 71, has vowed to turn up on Tuesday to be sworn in. Democratic leaders - along with Mr Obama - insist the appointment cannot stand, however, and have drawn up contingency plans to have the Senate sergeant-at-arms and even armed police block his entrance on the grounds that he will lack the required paperwork.

The scandal has become a distraction for Mr Obama as he begins talks to get an almost $1 trillion recovery plan for the stricken US economy through Congress quickly. Senate Republicans and some conservative Democrats are criticising the proposal for being too costly and too rushed.

On Monday Mr Obama will meet Democratic and Republican leaders to discuss the plan, which he wants to be able to sign into law almost as soon as he is sworn in on January 20. Yet with the dispute over his seat and the contest for the upper chamber's Minnesota representative still undecided, Mr Obama has only a 57-seat Senate majority, giving Republicans enough votes to slow the process down.

Mr Obama and his party oppose Mr Burris because he was appointed by Mr Blagojevich, who was arrested on December 9 on corruption charges including allegations that he tried to sell the vacant Illinois Senate seat of the President-elect to the highest bidder.

Mr Blagojevich is still the only man with the authority to name the replacement for Mr Obama, however. His brazen move this week to name Mr Burris has presented Democrats with a significant problem that is becoming more politically charged by the day.

Despite the appointment of Mr Burris being opposed by the President-elect, all Democratic senators, his state party and the Illinois secretary of state, it is far from clear that anybody has the constitutional authority ultimately to block it.

Democrats are also anxious about the chance of a confrontation on Tuesday because Mr Burris, who is not accused in any way of corrupt behaviour, is black. The last thing the party wants is to stop the entrance into the chamber of the man who would be the only African-American US senator.

Jesse White, the Secretary of State for Illinois, said that he would refuse to certify the appointment of Mr Burris. Mr Burris has already filed a lawsuit in Illinois trying to compel Mr White to sign the required documents.

Democrats have a number of options but all could face legal action by Mr Burris that could end in the Supreme Court. One is to refer his appointment to the Senate Committee on Rules, which could take months to decide the issue. By then, they hope, Mr Blagojevich will have been impeached, allowing his successor to name another replacement. Another option is to seat him, then expel him with a two-thirds vote.

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