Washington ? It’s a rare day when Sam Brownback is denounced as a radical left-winger.

But that’s what happened Tuesday on an issue that has riven the Republican Party and threatens to remain controversial through the 2008 presidential campaign: illegal immigration.

Brownback, the senior senator from Kansas and putative presidential hopeful, is considered among the Senate’s most conservative Republicans. His hopes for the GOP presidential nod rest largely on uniting conservative activists around his candidacy.

Nevertheless, he was the subject of a withering attack from the right leveled by Rep. Tom Tancredo, R-Colo.

Tancredo, chairman of the House Immigration Reform Caucus, slammed Brownback as “an extreme opponent of getting tough on illegal immigration” with a “miserable record.”

A Tancredo spokesman later upped the ante by calling Brownback “as left as they come on this issue.”

The source of Tancredo’s ire: Brownback’s support of a bill that would provide a yearslong path to U.S. citizenship for millions of illegal immigrants and create a guest worker program. The bill’s chief sponsors are Republican Sen. John McCain of Arizona and Democratic Sen. Edward Kennedy of Massachusetts. The bill would gut a tough House-passed reform bill, which has no guest worker program, offers no amnesty and is focused on securing U.S. borders.

Brownback responded in a statement: “The Senate Judiciary Committee has been hard at work for over a month on comprehensive immigration reform. No bill before the committee proposes blanket amnesty. … Border security is our main priority. We are working to merge the best of several proposals, and hopefully we can all agree that we must protect our borders, enforce the law, provide legal means for people to work in the United States, and fix a broken system.”