The weekend shutdowns of the no. 7 train that Queens residents and business owners say is having devastating effects on their lives and livelihoods, is only a taste of the service disruptions to come, transportation officials say.

The Metropolitan Transportation Authority plans to knock out weekend service on the no. 7 line this weekend for the third straight time, as well as the next four weekends, three more in November, and seven more in early 2008. The reason: to complete switch and signal upgrades on one of the oldest lines in the system.

After these track improvements are completed, the MTA is planning to bring computer-operated trains to the no. 7 line, which will require the agency to cut service again for at least 50 weekends over the next five years, according to transit sources. The award date for that project has been set for January 2008.

The computerized signal system, currently used to control only the L line, allows trains to run faster and closer together, thereby increasing service, the MTA says. Some transportation planners are raising eyebrows about bringing the expensive system to the no. 7 line when it is still in a test phase on the L line. The final estimated cost for the L line system is $278 million, which is $68 million over budget.

About 250,000 straphangers are estimated to ride the no. 7 line on an average weekend. Many are complaining that even with shuttle buses replacing subway service, travel times have quadrupled. Some Queens residents say they have forsaken the no. 7 line altogether and catch the Long Island Rail Road instead.

The no. 7 train is one of the most heavily trafficked lines in the system, because it connects Queens to Midtown Manhattan and offers connections to more than half a dozen train lines along the way.

“The people of Queens are growing accustomed to lousy 7 service, which is unfortunate because the 7 is a lifeline,” Council Member Eric Gioia of Queens said. “You can’t just walk to any street corner and hail a cab. We rely on mass transit, and when the no. 7 train is down, we suffer.” Mr. Gioia last week participated in a rally protesting the service cuts.

The MTA is assuring concerned riders that the short-term disruptions will bring better service down the road. “The cold weather hampered progress,” an MTA spokesman, Paul Fleuranges, said in an e-mail message, responding to the question of why there may be more service cuts than originally planned. “We have a recovery plan to make up for what we didn’t get done,” he wrote.