WASHINGTON – President Bush delivered his toughest words yet on border security and illegal immigration yesterday, telling an audience in Arizona that he will lead efforts at hardening the border and returning those who are caught crossing it.

But in reiterating his support for a guest-worker program that would include provisions allowing workers now here illegally to stay, Mr. Bush may have handed hard-line immigration opponents within his own party an issue to run on during next year’s congressional elections.

Republicans are divided over what to do at the Mexican border, where most of the roughly 500,000 aliens who come to America each year cross. A number of Republican congressmen face tough primaries next year because of the immigration issue, prompting leaders in the House of Representatives to press for legislation that focuses on tough border security.

The debate among Republicans in the Senate is focused on dealing with the estimated 11 million illegal immigrants who are already here. A bill sponsored by Senator McCain, a Republican of Arizona, and Senator Kennedy, a Democrat of Massachusetts, would allow workers to remain here if they pay a fee roughly equivalent to the cost that many pay to be shepherded across the border.

A tougher bill, sponsored by Senators Cornyn, a Republican of Texas, and Senator Kyl, a Republican of Arizona, requires all illegal immigrants who are now here to return to their native countries before they can reapply for a work permit. Under the bill, aliens who do not leave America would be ineligible to apply for a temporary work permit for 10 years.

In his speech, Mr. Bush sought to balance the concerns of House and Senate Republicans by outlining stricter border controls and by encouraging Messrs. Kyl and McCain, who attended the event at a Tucson military base, to come up with a compromise on dealing with illegal workers sometime in early 2006.

“We have a chance to move beyond the old and tired choices of the immigration debate and come together on a strategy to enforce our laws, secure our country, and uphold our deepest values,” Mr. Bush said. “We’ve made good progress, but you know like I know, there’s a lot more to be done.”

Mr. Bush’s plan for stronger border control includes termination of an existing “catch and release” program whereby captured aliens are released in anticipation of a court hearing to which roughly 75% fail to show up. The plan also calls for an additional 1,000 border control agents in 2006 and for pressing foreign governments to take back illegal aliens more quickly.

Much of the speech included proposals that Mr. Bush has already outlined, including legislation he signed last month that adds $139 million in border security technology upgrades and $70 million for the installation of border barriers and patrol roads in rural areas. Mr. Bush has also authorized the completion of a 14-mile barrier wall near San Diego.

Immigration proponents welcomed Mr. Bush’s speech, calling it his strongest statement on the issue yet. The deputy director of the National Immigration Forum, Angela Kelley, said Mr. Bush managed to come across as tough but balanced at the same time.

“He did tick off some very tough proposals,” Ms. Kelley said. “It would have been very disappointing if he had only pointed to the House proposal, but he seemed to give the Senate equal time. This was the most detailed the president has been about immigration in about two years.”

An immigration expert at the Manhattan Institute, Tamar Jacoby, said she was pleased by the way Mr. Bush framed the issue. “I think it’s very important,” Mr. Jacoby said of the speech. “This debate and any movement forward has to take place in a context of increased security and enforcement on the border because that’s what concerns the public the most.”

Still, those who have been most critical of Mr. Bush and Republicans on immigration found little encouragement in the speech. And their disappointment could mean that efforts to bridge the ideological divisions that have grown up around the issue may only intensify in the run-up to next year’s congressional elections.

A leading congressional critic of Mr. Bush’s immigration policies, Rep. Tom Tancredo, a Republican of Colorado, said Mr. Bush offered nothing new in his speech and predicted trouble for the Republican Party next year as a result.

“This speech was some pretty good meat that he put in between two pieces of stale bread,” Mr. Tancredo said. “He can’t continue to hand on to the guest worker program and expect to get any support from me. If you tell people they can stay here even if they’ve broken the law, that’s still amnesty. You can put as much lipstick on that pig as you want, but it’s still a pig.”

An independent pollster and political analyst, Stuart Rothenberg, said division over immigration among Republican will not necessarily hurt the party in next year’s elections. He said that Mr. Bush’s speech could, instead, give the party something to focus on other than the Iraq war, ethics scandals, or spending.

“There are people in the party who just want to talk about the jobs part of it, so it’s kind of a mixed bag,” Mr. Rothenberg said. “But, in sum, it probably helps the Republicans because it refocuses attention on security, and that’s probably better for Republicans than talking about the latest roadside bomb in Iraq or the latest problems they’re having with domestic spending.”