Maryland transportation officials said yesterday that a two-mile section of roadway on the Chesapeake Bay Bridge that cracked shortly after it was laid will be repaved by Thanksgiving with a different type of concrete.

Speaking before a special hearing of the Senate Budget and Taxation Committee, transportation officials said that several mistakes were made in the handling of a special type of material, called microsilica concrete, that was used so that construction could be done in cold weather to minimize the impact on summer beach traffic.

A preliminary report found that several steps in the handling of the microsilica concrete, including mixing and placing it in weather that was too cold even for that type of concrete, were not in accord with industry standards or the manufacturer's specifications.

Transportation Secretary Robert L. Flanagan also told lawmakers that fixing the problem will cost an undetermined amount more than the $7 million originally estimated because of increased costs related to preparation, scheduling and materials.

The Senate committee called the hearing after learning of problems last month on repaving the westbound span of the Route 50 bridge, part of a four-year, $60 million construction project that is still scheduled to be completed by Memorial Day 2006. Two inches of concrete were scraped off the road surface in preparation, and when the new concrete was poured, it failed to bond and began to crack.

Senators peppered Flanagan and other transportation officials with questions about how the bridge contract was crafted, why that cement was chosen and who would be responsible for the millions it will cost to rectify the mistakes. They also bemoaned the delays that the extra work would cause drivers on Maryland's gateway to the Eastern Shore and raised the possibility of higher bridge tolls.

State officials have warned motorists to expect major delays and congestion on the bridge, because the left lane of the westbound span will be closed until Nov. 24. Also, they have said that two lanes will be closed nightly starting at 8 and all three will be shut from 10 p.m. until 5 a.m. During those hours, two-way traffic will run on the eastbound span.

Several senators also expressed their displeasure over the resignation Monday of Thomas L. Osborne, executive secretary of the Maryland Transportation Authority. Osborne said in a statement Monday that a change in leadership would bolster public confidence in fixing problems with the bridge.

"I'm extremely unhappy he left," Sen. Ida G. Ruben (D-Montgomery) said during the hearing. "I hope he's not being made a fall guy."

Flanagan responded that Osborne had done "many, many excellent things" and that he decided to resign on his own.

Officials told the senators that they used the microsilica concrete because it is denser than regular cement and is supposed to reduce wear and tear. They said they had confidence in it because it had been used on two other state projects, although they acknowledged yesterday that neither of those presented the wind and temperature challenges of the high-arcing Bay Bridge.

Although officials have not concluded whether the substance itself is to blame, rather than its handling, they said they would use a latex-modified concrete on their second attempt to avoid repeating any mistakes.

Some senators said that the problems with handling the microsilica proved that the state wasn't liable for the mistakes. "The failure was in the application of the product," said Sen. Gloria G. Lawlah (D-Prince George's).

Flanagan cautioned that it was too soon to say where fault lay but that he is working with the state attorney general's office on a possible lawsuit to pay for the fixes. Flanagan also said the state would pay to repair the failed section pending a determination of who is to blame.

Senators were dismayed to hear that there was only one bidder on the project, because of its speedy time frame, and that the contractor was allowed to choose the material.

Flanagan also defended his decision to bring in a panel of experts to verify fixes proposed by state engineers, saying that "it appeared to me we needed a cross-check."

The four-year, $60 million construction project on the westbound span is set to be completed by Memorial Day 2006.