Citing differences over the hot-button immigration issue, U.S. Sen. John McCain has canceled today's campaign appearance for Brian Bilbray, GOP candidate for the 50th Congressional District.

Bilbray has publically criticized a bill McCain helped craft that would provide a pathway to legalization for millions of illegal immigrants.

In a Tuesday letter sent by e-mail to Bilbray's campaign, a spokesman for McCain's political action leadership committee, Straight Talk America, wrote that McCain was canceling his appearance "to avoid distracting from the overall message of the Bilbray campaign.

"The Senator and Brian may disagree on some of the issues related to immigration reform," wrote Craig Goldman, who could not be reached for comment Tuesday.

While the e-mail did not specify what those issues might be, Bilbray said Tuesday that he believes the reason for the cancellation was their differences over language in the McCain bill that Bilbray believes amounts to amnesty for those who have broken the law.

"We agreed to disagree," he said of his differences with McCain over the issue.

In a Tuesday news release, a spokesman for Francine Busby -- Bilbray's Democratic opponent in a June 6 runoff election to pick a temporary representative for the seat through the end of the year -- noted that Busby supports the McCain immigration plan.

Last week, the U.S. Senate passed an immigration reform bill that would allow some of the estimated 12 million illegal immigrants living in the United States to legalize their immigration status.

An earlier version of the legislation was sponsored by McCain and Sen. Ted Kennedy, D-Mass., but failed to pass muster in the Senate. However, Sens. Chuck Hagel, R-Nebraska, and Mel Martinez, R-Florida, included several provisions of the McCain bill in the latest version of the proposed legislation. The new bill includes language spelling out who would be eligible for legalization and under what circumstances.

It allows illegal immigrants who have lived in this country for more than five years to start the legalization process if they pass background and health checks, learn English, pay fines and back taxes and stay employed.

Those who have lived here for two to five years would have to leave the country briefly before re-entering on a guest worker program and then be allowed to begin the legalization process. Those illegal immigrants who have been in the country for less than two years would have to leave the country.

A House version of the bill was approved in December that did not include a guest worker provision or a mechanism for illegal immigrants living here to legalize their status.

Bilbray has said he strongly opposes the Senate version and supports the House version of the bill. The competing bills will now go before a conference committee made up of lawmakers from both houses to try and hammer out a consensus version of the legislation.

Bilbray said that in earlier contacts with McCain's office, he made it clear that "the issue of illegal immigration is THE issue in this campaign, and the Senate version has amnesty and allows those here illegally to buy citizenship," Bilbray said.

After McCain's last-minute cancellation, Bilbray said his staff contacted U.S. Rep. David Dreier, R-San Dimas, and asked if he could fill in at today's fundraiser for Bilbray at the Westgate Hotel in downtown San Diego.

Dreier, who also serves as chairman for the powerful House Rules Committee, had a bill before the House last year that called for a high-tech Social Security card that immigrants would have to present to prospective employers before getting a job. The House immigration-reform bill approved in December included language calling for a review of Dreier's proposal.

Dreier "was open … so he created a slot and moved into it," Bilbray said, adding that U.S. Rep. Duncan Hunter, R-El Cajon, will also be speaking at today's $250-a-plate campaign breakfast.

Contact staff writer William Finn Bennett at (760) 740-5426, or wbennett@nctimes.com.