San Francisco will borrow $260 million to complete a transit hub that’s over budget, city officials said Monday. The short-term variable-rate certificates will be purchased by the Metropolitan Transportation Commission and Wells Fargo & Co. to complete the first, $2.3 billion phase of the Transbay Transit Center, Mayor Edwin Lee’s office said in a statement. Rising construction costs have added $700 million to the project, which is designed to link 11 transit systems in eight Bay Area counties. “The Transbay Transit Center is an absolutely critical part of the future of our regional transportation system,” Scott Wiener, member of the city’s board of supervisors, said in the statement. “If we allow this project to fail, we will pay a far higher price in the long-term.” The loan will be repaid by special taxes and increased tax revenue generated in the district where the transit hub is located. The city and transit commission have proposed measures to improve oversight and management of the project, including the public works department assuming construction management. The Cesar Pelli-designed hub, a joint venture among the city and county and local transportation agencies, is intended to evoke the grandeur of New York’s Grand Central Terminal. The transit center, funded with a mixture of sources including federal grants and loans, sale of prime downtown property and local taxes, is scheduled to open its first phase, a new bus depot, next year. A second phase, which could cost nearly $4 billion, would bring in regional Caltrain lines and a proposed high-speed rail. The goal is to ease congestion for the region’s 8.6 million residents by linking mass transit systems.