Businesses have boosted moderately their investment plans for the second half of the year, the Department Commerce reported yesterday.

The administration said the rise bespeaks increasing confidence in the economic future on the part of business executives.

But a leading business spokesman said that government's survey of plant and equipment spending plans is weak, attesting to "a future weakening of the economy in the second half of 1977."

In other economic developments yesterday:

The Federal Reserve Board reported that consumer borrowings increased by $2.32 billion in July, about the same as in June. Consumers repaid $16.1 billion of their outstanding debt in July, but borrowed $18.42 billion.

Henry Kaufman, vice president of the investment banking firm of Salomon Brothers and one of Wall Street's most respected money market analysts, said that short-term interest rates will continue to rise over the next year. Kaufman his remarks in London.

The Commerce Department survey taken in July and early August, reported that businesses expect to spend $136.5 billion in 1977 for plant and equipment, up 13.3 per cent from 1976. An earlier survey had predicted business capital spending increases of 12.3 per cent this year.

The administration is counting on increases in business investment to carry on the economic expansion, which has faltered in recent months as consumer spending and business inventory accumulation leveled off.

The department said that actual business investment spending rose 3.1 per cent in the second quarter of the year to a seasonally adjusted annual rate of $134.24 billion, and is expected to rise another 3.1 per cent in the third quarter to an annual rate of $138.43 billion.

The increase will slow 2.6 per cent in the fourth quarter, with investment planned at an annual rate of $142.02 billion. The actual investment for the year will be $136.5 billion, the survey predicted.

Secretary of Commerce Juanita Kreps said that the upward "adjustment in business plans for spending on new plant and equipment suggests that business executives are becoming more confident about the performance of the economy in future years. During the rest of the year, business fixed investment expenditures will be providing somewhat more stimulus than previously estimated."

She called the increase "an encouraging development in a sector that had been lagging."

But Jack Carlson, chief economist for the U.S. Chamber of Commerce said that the slowing in capital investment growth from 3.1 per cent in the third quarter 2.6 per cent in the fourth quarter is a bad sign.

"The news of the past weeks - higher unemployment, a decline in the leading indicators and now a slowdown in investment intentions by the fourth quarter of 1977 - would indicate growing economic problem and the need to stimulate investment," Carlson said.

The Carter administration had said that the economy is in a "temporary lull" that it should break out of shortly. It still says it expects the unemployment rate to fall to near 6 per cent by the end of the year. It was 7.1 per cent up from 6.9 per cent in August.

While Salomon Brothers' Kaufman was predicting higher interest rates. George R. Baker, executive vice president of the company that owns Chicago's biggest bank, said in London that he expects major banks to boost their prime rates from the current 7 per cent level to 7.25 to 7.5 per cent by the end of the year.

Prime rates, the interest bank charge their best corporate customers for short-term loans, should rise to 3 per cent next year, said Baker, of Continental Illinois Corp.

Salomon predicted that the federal funds rate, the interest banks charge each other for overnight loans excess reserves, will range between 7 and 7.5 per cent next year compared with the current 6 per cent level. Last spring, the federal funds rate was near 4.5 per cent.

In another development. Harvard economist John Kenneth Galbralth meeting of savings and loan executives in San Francisco that wage and price controls are the only way to stop the current inflation, a position he had held for years.