WASHINGTON -- President Bush plans to use the port of Baltimore as a backdrop tomorrow for a speech calling on Congress to extend provisions of the USA Patriot Act, the post-9/11 law that grants the government broad powers to fight terrorism.

During his morning visit, Bush will highlight stepped-up efforts to secure the nation's ports. He is to be given a demonstration of a new, high-tech container-scanning device in use at the Seagirt Marine Terminal before making remarks to an invited audience at the Dundalk passenger terminal.

In the nearly four years since the Sept. 11 attacks, port security has been overshadowed by efforts to secure the nation's air transportation system. A $31.8 billion spending bill for homeland security, approved last week by the Senate, included a $50 million increase for port security grants in 2006, up from $150 million this year.

Critics in Congress, who have pushed unsuccessfully for more spending for port security, say the nation's ports are easy targets. A report this year by the Government Accountability Office said U.S. ports remain vulnerable to terrorism, despite increased spending and security efforts.

Nearly 140,000 cargo containers are shipped to Baltimore each year, according to port officials. About one in seven containers, or 14 percent, are examined by screening devices for bombs or other material.

State officials have acknowledged shortcomings in security on the docks of Baltimore, the country's eighth-largest port. A recent report in The Sun revealed gaps in fences, unattended gates, security systems that don't work and a lack of round-the-clock boat patrols.

Baltimore has received $14.5 million in federal port security grants since 2002, and officials say the port is more secure today than before Sept. 11, 2001.

Among the new tools at the port is an X-ray machine used to scan cargo containers. The $6 million device, a more powerful version of those used at airports to screen baggage, can see through a foot of steel.

Last month, Gov. Robert L. Ehrlich Jr. was on hand for the first public demonstration in Baltimore of the device. Peter Kant, vice president of government affairs for Rapiscan Systems, which manufactures the machine, said the company was "very happy" that Bush would be getting a first-hand look.

The president's primary purpose for the visit, White House officials said, is to prod Congress to make permanent 16 expiring provisions of the Patriot Act, enacted shortly after the Sept. 11 attacks to broaden the government's investigative powers to fight terrorism.

Civil liberties advocates have denounced major elements of the act, parts of which are to expire at the end of this year, calling them infringements on citizens' rights.

Lawmakers have balked at granting Bush all of the powers he has requested, and Congress is moving to curtail some provisions or make them temporary.

The House is expected to approve as early as tomorrow a version of the measure that would put a 10-year limit on two of the most contentious provisions, unless a future Congress renews them. The first allows "roving" wiretaps, which let investigators tap any phone a suspect is using; the other allows the FBI to seize a wide variety of business records with the approval of a judge.

Also among the contentious parts of the Patriot Act are provisions that allow the FBI secret access to library and medical records.

Renewing the measure is a top priority for Bush, who said at the FBI Academy in Quantico, Va., this month that the terrorist threat "will not expire at the end of this year, and neither should the protections of the Patriot Act."

Bush contends that the measure protects civil liberties and that no abuses have been reported since its enactment.

The Patriot Act "closed dangerous gaps in America's law enforcement and intelligence capabilities -- gaps the terrorists exploited when they attacked us on Sept. 11," Bush told Ohio State Patrol officers last month, calling it "the considered response of a nation at war."

Sun staff writers Gwyneth K. Shaw and Meredith Cohn contributed to this article.