Can 11 million jobless + decaying roads, bridges = job opportunities?

America is experiencing the worst unemployment rate in 42 years, while its roads, bridges, ports, and sewer and water systems - what economists call the ''infrastructure'' - need an estimated $2.5 trillion worth of repairs.

Can unemployed workers be brought to these jobs? Some call it the biggest challenge to government since the Great Depression.

The jobs problem in America may decide the November election - although many think it transcends normal economic explanations and is here to stay. Some think it may require new initiatives by the government like the New Deal introduction of the Works Projects Administration. More recently the government bailed out the Chrysler and Lockheed corporations. Some argue the government ultimately must intervene.

One proposal is for a ''capital budget'' to channel funds to the infrastructure.

In folksy terms, an article in the Wall Street Journal (Oct. 1) cites towns and villages over the nation where bridges, highways, or sewers are getting old. In Arkansas, 2,000 rural children walk over 45 old bridges unsafe for buses, it says.

US News & World Report (Sept. 27) says that rebuilding the infrastructure is a $2.5 trillion job - ''bridges, ports, roads, sewage disposal - these and other underpinnings of US life and economy are eroding from long neglect. Repairs will be costly. But, say experts, more delays could be disastrous.''

Newsweek magazine (Oct. 18) in a cover story on ''Jobs: How to get America back to work'' concludes that uncoordinated government effort ''is no longer enough.

''The profound changes at work in the job market require a new era of cooperation among all sectors of society, a rigorous attention to preventing the economic and human pain of sweeping dislocation.''

America has completed 42,944 miles of the interstate highway system begun in the 1950s - the greatest web of highspeed boulevards in the world. But 2,000 miles ought to be repaired or repaved every year and currently an estimated 8, 000 miles are crumbling away and must be resurfaced. According to a new congressional study, the cost of renovating and completing the highways is $54.8 billion.

How is it to be done? Can America's jobs and its unemployed be brought together? The question will last longer, many argue, than through the present election, in which Mr. Reagan defends his program and Democrats attack it.

In an editorial Oct. 11, the New York Times says the proposal by New Jersey's Gov. Thomas Kean for the establishment of an ''infrastructure bank'' to mobilize capital resources and ease the burden of communities is a good one. The editorial argues that Governor Kean is on the right track: ''New Jersey, like most other states, must be rebuilt, with or without much help from Washington.''

One challenge facing such proposals is a shift in philosophies: President Roosevelt adopted a philosophy of centralized government that overthrew ''laissez faire.'' With 25 percent of the labor force unemployed, the nation grabbed it, though the Depression wasn't fully overcome until the United States entered World War II. Now President Reagan leads a move against centralization, arguing that the federal government has gone too far. He would turn some responsibilities back to cities and states.

Simultaneously, industry itself has changed from mass-production ''smoke-stack'' factories to more technical and service jobs, leaving millions of workers idle. Currently, 11 million people are unemployed; 1.6 million more have been out of work so long that they've quit looking for jobs.

Industry is churning with new jobs but also with discarded semi-skilled workers. Many unemployed have exhausted their normal 39 weeks of benefits. Between 1976 and 1980 an estimated $16 billion went to such benefits. Budget constraints prevent Washington policymakers from extending them. Change comes rapidly. Unemployment has sent up social problems in many communities. Crime has increased.

America has priced itself out of the international market in some products. Far-reaching changes are seen in the new ''post-industrial'' era with a threat to the blue-collar middle class. For example General Motors, with 130,000 workers already laid off, decided last spring to install 14,000 industrial robots over a 10-year period. One estimate is that they can replace 40,000 workers.