Fairfax County has suspended work on the last leg of a nearly $43 million contract to overhaul its computer systems after technical problems threatened to push the project further over budget, county officials said Thursday.

The ambitious effort — the implementation of which had been overseen by the man recently appointed county executive, Edward L. Long Jr. — has been marred by delays and glitches, according to an April 6 letter sent to the software company from the county’s Department of Purchasing & Supply Management.

In the letter, the county advised SAP Public Services of its intent to suspend all work on the third phase of its Fairfax County Unified System project, known as FOCUS. The new system is intended to save money by consolidating purchasing and other administrative procedures in a single database serving both the county and Fairfax County Public Schools.

The county decided to suspend work after the software company requested “extraordinary additional costs” for the third phase, even as the county struggles to iron out problems with earlier phases, according to the letter. SAP’s request to bill an additional 11,000 hours for technical support — well above the 7,300 hours included in the base contract — is “improper,” the county says in its letter.

The letter also notes that bugs in the new system caused a four-month delay from its scheduled launch last July and have continued to pop up since the system became operational Nov. 7.

“The simple process of ordering paper is now a major ordeal,” Supervisor Pat S. Herrity (R-Springfield) said.

Cathy A. Muse, a county purchasing agent, said Thursday that SAP’s request for additional hours for the third phase would cost an estimated $3.9 million. That’s in addition to the $3.4 million extra the county agreed to pay in September, increasing the total cost to $42.4 million. Of that, the county already has paid $17.5 million, Muse said.

David Molchany, a deputy county executive who assumed control of the FOCUS project last week, said the county is weighing whether to proceed.

Members of the Board of Supervisors said that such a massive overhaul was bound to encounter some glitches, but they blamed SAP for continuing problems and said it should not reflect badly on Long.

“[Our] leadership team has stepped forward and said, ‘We’ve got a problem and we’ve got to address it.’ And I think that’s to its credit,” Supervisor Michael R. Frey (R-Sully) said. “It’s not like you can just throw one [system] out and put another one in.”

Long, a former chief financial officer and deputy county executive, was brought back last year after retirement and given sweeping authority to oversee the installation of FOCUS. On April 10, the board appointed him to succeed County Executive Anthony H. Griffin, who plans to retire next week. Long takes over April 25.

On the day that Long was appointed last week, he acknowledged that the FOCUS project had encountered delays and problems. But he said that the county was on track to implement the next phase by July and called the project a “success.”

“There have been growing pains,” Long told reporters. “[But] I think we’ve done a good job to get to where we are.”

“You have to put the problems in perspective,” Long said Thursday night. The county decided to alter some of its business practices to conform to the demands of the new computer system because the county did not want to pay to customize software, and the workforce of approximately 12,000 is doing its best to adapt, Long said.

“Sometimes it’s not a problem, it’s a comfort issue,” Long said. “So when I said the project has been a ‘success,’ we’ve been able to pay our bills and process things. But it’s only been five months. This is not a project that’s out of control. It’s not a project that’s millions and millions of dollars over budget.”

The county reviewed its computer systems for vulnerabilities amid widespread concern that computers might freeze with the changeover in dates at the end of the last millennium. After deciding the systems needed upgrading, county officials signed SAP contracts in 2009 for software and in 2010 for its installation.

“It’s been more complicated in its implementation than everyone thought at the beginning,” Board of Supervisors Chairman Sharon Bulova (D) said.“Ed is a very solid individual, and I think because of Ed’s experience with FOCUS and his knowledge of FOCUS, I think as county executive he’ll have more opportunity to work things out with FOCUS.”

SAP Public Services is a unit of SAP AG, a global German software company whose U.S. headquarters is located in Newtown Square, Pa.

“I don’t want to get into whose fault this is,” said Andy Kendzie, a spokesman for SAP. ‘Whatever issues are going on with Fairfax County, we want to work with them to get them solved.”