The Republican hold on both houses of Congress is expected to tighten in the elections. All 435 seats in the House and 34 of the Senate's 100 seats are up for grabs.

``The typical mid-term result is that whatever party is in the White House is going to lose seats in the House,'' Columbia University political science professor Robert Shapiro said.

``Around 20 is average, so anything less than a 20-seat loss might be a victory for the Democrats,'' he added, pointing to a 10-seat drop as ``a good showing for them''.

Going into the contest, Republicans held a 228-206 seat advantage in the 435-member House of Representatives -- which has one independent -- and accounted for 55 of the 100 Senators.

At issue for the minority party is its ability to influence theagenda set by the Republicans who, if they win enough seats, could override Democratic efforts to block or modify legislation.

A strong Republican showing could also hurt Clinton, who faces just the third presidential impeachment probe in US history, by energising his foes and weakening his Congressional allies.

Clinton has maintained high job approval ratings among Americans, despite a lurid report from independent counsel Kenneth Starr packed with sexual details of the affair between the president and the intern. The report charges that Clinton committed 15 impeachable acts in his denial under oath of the affair.

The Republicans could read a resounding victory as the public's go-ahead on impeachment matters, and could prompt them to take steps that may threaten Vice President Al Gore's 2000 presidential ambitions.

A big win may also prompt Republicans to appoint a special prosecutor to look into allegations that Gore broke US campaign finance laws during the 1996 race, keeping allegations ofmisconduct on the front burner at least for months.

``The most damaging thing for Gore out of this is not anything that happens on election day, but will there be a special prosecutor appointed to look into campaign financing?'' said Middlebury College political science professor Eric Davis.

``If the Republicans don't do well, it makes a special prosecutor less likely to look into Al Gore or other Democrats,'' said Shapiro.

The good news for Clinton's party is that ``there's a sense of dissatisfaction with the Congress and some Democratic challengers may be able to get some positive mileage,'' said Davis.

And the solid US economy could also help the Democrats: ``Historically, when voters take performance of the economy into account, they're more likely to vote for the president's party,'' he added.

Citing a recent US Federal Reserve interest rate cut, which is likely to buoy the economy, Davis said: ``If the Democrats' losses are less than expected, (they) may have (Fed chairman) Alan Greenspan tothank.''