As a spur to investment and the lagging productivity of American industry, a bipartisan group of senators and congressmen yesterday proposed that all businesses be allowed extremely rapid tax write-offs for almost all capital investments.

The change, which would eliminate the president link between the useful life of an asset and the rate at which it is depreciated, would cut business income taxes by $5 billion in the first year, and by $30 billion after a five-year phase-in period.

Businesses could recover investments in structures, including commercial office buildings, over 10 years, equipment in five, and cars and light-duty trucks in three. The equipment would qualify for the full 10 percent credit and cars and trucks for a 6 percent credit.

Most of the benefits of the proposed changes would flow to industries with long-lived assets. Office buildings, for instance, now must be depreciated over 40 years instead of 10.

Pipelines, water transportation equipment, cement and steel production equipment - all now must be depreciated over a minimum of 14 1/2 to 17 1/2 years. That would drop to five.

On the other hand, the textile industry, with a seven year life for much of its equipment, would get little benefits from the change, tax experts pointed out.

According to an analysis by Data Resources, Inc., an economic consulting firm, the new system would lead to an added $50 billion in capital investment over five years, the sponsors said.

The process of depreciation, or writing off an investment, involves counting a portion of the original cost us an expense each year that the building or equipment is in use until the accumulated depreciation equals that cost. As an expense, depreciation reduces profits and therefore business income taxes.

"Our aim in introducing this legislation," said Rep. Barber Conable of New York, the ranking Republican on the House Ways and Means Committee, "is to overhaul completely the antiquated system of depreciation currently embodied in the tax code."

The link to "useful lives" of assets has worked to inhibit investment and capital formation in the U.S., Conable said. "This chronic low level of investment has resulted in sagging productivity, sluggish industrial production, and faltering competitiveness in world markets."

Another backer, Rep. James Jones (D-Okla.) an influential member of Ways and Means, said the measure was "arrived at through a process of elimination" during extensive discussions with a large number of business groups.

"There are other alternatives, but none has such wide support," Jones said.

Among those backing the bill are the National Association of Manufactures, the U.S. Chamber of Commerce, the National Federation of Independent Business, and the Business Roundtable, a group comprising many of the country's largest corporations.

Basically, the sponsors want to make the proposal the business portion of the next tax cut bill, whenever that should come.

One Carter administration tax official noted that President Carter has said he would not support a tax cut in either 1979 or 1980, but he added, "When there is next an income tax cut, faster depreciation is surely one of the items that should be considered."

Both Federal Reserve Chairman G. William Miller and presidential inflation adviser Alfred Kahn have suggested that the most useful type of business tax cut in terms of spurring investment would be stepping up depreciation rates. CAPTION: Chart, Capital Cost Depreciation, The Washington Post