WASHINGTON - Reaching for history, President Obama yesterday nominated U.S. Appeals Judge Sonia Sotomayor to be the first Hispanic justice on the Supreme Court, championing her as a compassionate, seasoned jurist whose against-the-odds life journey affirms the American dream.

Republicans, many of whom see her as too liberal, will have to decide whether to make a fight of her confirmation. However, rejecting Sotomayor's nomination would be difficult in the heavily Democratic Senate. Even a major effort to block her confirmation could be risky for a party reeling from losses in last year's elections.

Hispanics are the fastest-growing segment of the population, increasingly active politically, and turning increasingly to the Democrats.

Obama beamed as he introduced Sotomayor as a judge who displays both an impressive mind and heart and a jurist who takes on cases with "an understanding of how the world works and how ordinary people live."

The White House tableau itself exuded history in the making: an African American president and his white vice president, Joe Biden, striding onto a stage in the ornate East Room with the nominee who grew up in a New York housing project where her parents had moved from Puerto Rico.

At 54, she would join Ruth Bader Ginsburg as the second woman on the court and just the third in its history.

She would replace moderate-liberal Justice David H. Souter, thereby likely to keep the court's ideological balance unchanged.

In fact, Obama might not get a chance to tip the balance for some time. The two oldest members of the court are liberal or left-of-center votes: John Paul Stevens, 89, and Ginsburg, who is 76 and recovering from cancer. The oldest conservative on the court is Antonin Scalia, 73.

A number of important cases have been decided by 5-4 votes, with conservative- and liberal-leaning justices split 4-4 and Justice Anthony M. Kennedy usually the decisive vote.

But if confirmed, Sotomayor would change how the court looks.

"With eight men, one woman, and no Hispanics currently sitting on the court, President Obama listened to voices like former Justice Sandra Day O'Connor in recognizing that diversity on the bench is essential," said Sen. Barbara Boxer (D., Calif.).

Fair hearing

Senate Republicans pledged to give her a fair hearing but cautioned they would question her rigorously and not be rushed.

The president, whose approval ratings trump those of Congress, challenged the Senate to confirm her before its August break. The Supreme Court begins its new term in October.

Democrats control 59 votes in the Senate - not counting Democrat Al Franken, who is leading in the disputed Minnesota Senate election but not seated. That is more than enough to confirm Sotomayor but not quite enough to stop a vote-blocking filibuster if Republicans attempt one.

The top Senate Republican, Mitch McConnell of Kentucky, said: "We will thoroughly examine her record to ensure she understands that the role of a jurist in our democracy is to apply the law evenhandedly, despite their own feelings or personal or political preferences."

In one of her most notable decisions as an appellate judge, she sided last year with the City of New Haven, Conn., in a discrimination case brought by white firefighters. The city threw out results of a promotion exam because too few minorities scored high enough. Coincidentally, that case is now before the Supreme Court.

Her ruling drew criticism from conservatives and is likely to play a role in her confirmation hearing.

Irking conservatives, Sotomayor also has said personal experiences "affect the facts that judges choose to see."

"I simply do not know exactly what the difference will be in my judging," she said in a 2001 speech. "But I accept there will be some based on my gender and my Latina heritage."