Democratic gains in the House and Senate are likely to further entrench the nation's divided government and escalate partisan strife between Congress and President Bush through the 1992 presidential election.

While the number of new Democratic seats is relatively modest -- one in the Senate and at least nine in the House (including one independent who will caucus with Democrats) -- the victories are expected to embolden Democrats to take on Bush more often in the second half of the president's term.

"It's likely to be more confrontational, more conflictual, more partisan and less oriented toward getting legislation through than differentiating their positions," said Thomas E. Mann of the Brookings Institution.

"The differences will be brought into sharper focus in the next Congress," Senate Majority Leader George J. Mitchell (D-Maine) pledged yesterday.

Democratic leaders attribute their electoral advances to the way they painted Bush and the Republican Party as defenders of the rich and themselves as champions of the middle class during this year's prolonged debate over reducing the federal budget deficit. They hold that view even though interviews with voters leaving the polls Tuesday suggested that while voters tended to identify the GOP as the party of the rich, the perception did not appear to be a major factor in any races.

"It doesn't substantially change their voting strength, but they feel they have the upper hand in public relations right now," Steven Smith, a University of Minnesota political scientist, said of the Democrats. "That may lead them to be more assertive and take more risks."

Congressional Democrats will not wait long to challenge the president. Shortly after returning to Washington in January, House leaders are expected to press a vote on a measure that would impose a surtax as high as 10 percent on millionaires. Bush adamantly rejected that sort of assessment during this year's budget talks.

In addition, House Speaker Thomas S. Foley (D-Wash.) has already pledged to make civil rights legislation a top priority next year. Bush vetoed a measure designed to expand the rights of those claiming to be victims of job discrimination. The Senate failed to override the veto by a single vote. Sen. Rudy Boschwitz (R-Minn.), the only Senate incumbent to lose Tuesday night, voted to reverse the veto but only after it was clear the override effort would fail.

When the 102nd Congress convenes at noon on Jan. 3, it will look much like the 101st Congress that adjourned in the early-morning hours of Oct. 28.

"They're going to pick up where they left off," said Richard F. Fenno Jr., a congressional scholar at the University of Rochester. "The president has got to decide how to get his party back together again and the Democrats have to decide how much they're going to push the advantage they have on the tax business."

In the House, Democrats added at least nine seats to their already commanding, 83-seat majority. While relatively small compared to previous midterm election gains by parties that did not hold the presidency, the shift leaves House Republicans at one of their lowest points in nearly two decades.

All but one senator seeking reelection prevailed. The upset victory of political scientist Paul Wellstone (D) over Boschwitz increases the Democrats' control of the Senate by one seat, 56 to 44.

Although still not enough to allow the Democrats to reverse a presidential veto or to stop a filibuster by themselves, the additonal seat could create "a nagging problem" for Bush by threatening the sometimes narrow margins by which the Senate has upheld his vetoes, according to Norman J. Ornstein of the American Enterprise Institute.

While the budget agreement sought to forge fiscal peace through the 1992 elections, Democrats are likely to press differences in such other areas as banking regulation and education. "In social policies and regulatory areas that don't involve much spending, expect to see continuing conflict," Smith said.

The lesson of Tuesday's returns was that "the philosophy that the best political strategy was to have a muddled message, blurring distinctions with Republicans, has been repudiated," said Rep. Robert G. Torricelli (D-N.J.).

But the Democratic gains were hardly an "overwhelming affirmation" of their positions, Ornstein said. "The attitude will be less aggressive, less partisan" than if they had gained 15 to 18 seats in the House and three or four in the Senate, he said. Still, "Democratic gains will make the president's life more difficult, no question about it."

Democratic leaders noted that in the Senate most incumbents who had been singled out by Republicans for strong challenges ended up winning by double-digit margins. Five of the GOP incumbents who were returned to office, on the other hand, had winning margins of less than 9 percentage points.