Obama's Supreme Court nominee expected this week

* Key Democrat says Obama likely to pick nominee this week

* Republican says his side lacks votes to block pick

By Thomas Ferraro

WASHINGTON, May 24 (Reuters) - U.S. President Barack Obama will likely announce a nominee within days to replace retiring U.S. Supreme Court Justice David Souter, Assistant Senate Democratic leader Dick Durbin said on Sunday.

"I've been told it is likely to come this week, but I don't know which day," Durbin told NBC's "Meet the Press" as the president entered a fourth week of considering possibilities.

Senate Republican Whip Jon Kyl, on "Fox News Sunday," admitted his party lacks the votes to block the pending nominee with a procedural hurdle in the Democratic-led Senate.

But Kyl also made clear Obama's pick will face plenty of questions. "Undoubtedly this nominee will be liberal," said Kyl, a conservative.

Obama has been mulling a short list of mostly women for a seat on the nine-member, male-dominated high court, which decides abortion, death penalty and civil rights cases as well as ones involving business and property rights.

The pick is unlikely to change the ideological makeup of the nation's highest court since Obama, a Democrat, is expected to select a liberal in the mold of Souter, who announced his resignation on May 1.