Nothing is forever. Concrete eventually crumbles. Even steel yields ultimately to fatigue.

America's monument to mobility -- our far-flung and highly prized national highway system -- is showing the wrinkles of middle age and the strain of billions of miles of travel.

The issue is one of immediate national concern. A flawed highway system impairs the nation's commerce, impedes productivity and increases transportation costs. America's 148 million motorists pay a heavy price for damaged roads -- in longer travel times, in ruined tires and in vehicle repairs.

Over the past 25 years, we have spent more than $70 billion constructing 40,700 miles of Interstate highway, with another 1,700 miles still to go. Billions more have gone into the other 3.9 million miles of roads and streets, and the hundreds of urban transit systems throughout our country.

For most of this century, we have funneled funds into road construction with scant concern for the inevitable consequences of wear and tear, weather and traffic levels that have repeatedly exceeded estimates.

Now our great highway system is faltering. Bridges are creaking. Pavement is cracking. Portions of the Interstate, our most traveled road system, are coming apart. Motorists crossing the Wilson Bridge have grown accustomed to catching glimpses of the river below through gaps in the bridge decking. Truckers on sections of I74 in Illinois drive well under the speed limit on what they call the nation's only "all gravel" Interstate. Elsewhere in America there are wooden bridges so old that schoolbus drivers walk their passengers across before driving the bus to the other side.

In our major cities, commuters ride rail cars that would be more at home in museums than on urban rights-of-way. Nearly 15,000 mass transit rail cars will reach retirement age during the next 10 years, and in many urban communities, transit operators routinely work overnight repair miracles on aging buses.

Still, we have a transportation system unequaled in the world. Most of it works wondrously well, most of the time. We have good roads, but they will remain good only if we maintain them. What we are seeing today are the early signs of a gathering storm. The 10 percent of the Interstate in need of resurfacing symbolizes the extent of the decay now eating away at the nation's infrastructure. Like the first stages of a creeping and potentially crippling disease, today's proliferating potholes and rusting bridges warn us that preventive measures are due, if not overdue, and that the price of delay could be catastrophic.

The program President Reagan outlined last Tuesday addresses the issue head-on. It provides the much-needed solution to the deterioration of the transportation facilities all of us use and all of us depend on every day. As the president said, the program is not a jobs measure -- although it will help employment. It is not a partisan political issue; there is strong support in Congress by members of both parties. It is not even a program for which there is a reasonable alternative. Repairing our transportation system, as the president said, "is a necessity."

It has become a necessity partly because age and use take their toll, partly because the value of the longstanding 4-cent federal tax on motor fuel has been steadily reduced by inflation, and partly because the revenues from that tax have been declining as motor vehicle fuel efficiency improves. The Highway Trust Fund, where the gasoline tax and other highway user fees are channeled, paid out $3.3 billion more than it took in during the past two years.

Under the administration's proposal, user fee revenues will be increased by the equivalent of five cents a gallon, for an additional $5.5 billion a year. We propose to dedicate at least $4.4 billion of that to highway and bridge projects, while making $1.1 billion available for capital assistance to public transit.

The increase in highway funding will enable us to accelerate construction on the unbuilt portions of the Interstate, reducing completion costs by an estimated $2 billion. It will more than double the funding available for the most pressing highway and bridge rehabilitation projects. It will let the states begin work almost immediately on several billion dollars worth of road and bridge improvement projects that have been on the shelf for want of funds.

We are recommending that a penny's worth of the increase -- about $1.1 billion a year -- go to the cities and states in block grants for capital assistance to meet urban transportation improvement needs. We must recognize today that our highway and transit needs are not mutually exclusive, but part of the same problem. That problem is urban mobility. The only alternative to the rehabilitation of existing public transit systems may be urban freeways that the community cannot afford or will not accept. Improved transit reduces congestion, and shrinks the demand for costly metropolitan expressways and the parking facilities that must accompany them.

We have learned that we cannot escape the consequences of time and use on our transportation facilities, but we can correct them. Deferred maintenance is the most expensive maintenance. We cannot ignore the fact that unless we deal now with the relatively moderate costs of resurfacing and rehabilitation, we will inevitably pay the higher costs of replacement and reconstruction.

There are other costs chargeable to delay. If highway conditions were allowed to continue to decline at present rates, the average motorist's costs could be expected to increase by as much as 25 percent by 1995. The 5-cent fee increase we are proposing, on the other hand, will cost the average driver only $30 more a year -- or about the price of a shock absorber.

We have enjoyed tremendous success in the United States with our pay-as-we-grow highway construction policy. It is now time to demonstrate that we have the means, and the resolve, to protect what we have created. We can do that only if we generate the resources, and structure a highway program, as committed to the preservation of our system as we have been to its development.