BALTIMORE, NOV. 2 -- A government witness said today that Wedtech Corp. officials gave Clarence M. Mitchell III a $50,000 check to prompt a congressional investigation of a competitor so the New York defense contractor could get a large Army contract the competitor had won.

The testimony, from Lawrence J. Shorten, a former Wedtech senior vice president, was the first to tie Clarence Mitchell to the payment, which federal prosecutors allege was part of $110,000 the former state senator and his brother, state Sen. Michael B. Mitchell, received to manipulate the House Small Business Committee headed by their uncle, then-Rep. Parren J. Mitchell (D-Md.).

The trial of the Mitchell brothers in U.S. District Court here on charges of obstructing a congressional investigation and wire fraud connected to their alleged dealings with the New York company entered its second week today.

Before Shorten testified, other government witnesses told the jury that Wedtech officials paid Michael Mitchell and his brother $50,000 to block their uncle's investigation of the company in October 1984, and had paid the Mitchell brothers an additional $10,000 to do further work to stop the probe when it resurfaced in March 1985.

Shorten testified that he, Wedtech Chairman John Mariotta and company officers Mario Mareno and Anthony Guariglia met with Clarence Mitchell in February 1985 to discuss undermining Ernie Green Industries, an Ohio firm, by prompting a congressional probe of that firm's qualifications as a minority contractor.

"We said we had another problem, and discussed, more or less, what to do about Ernie Green," Shorten testified.

"Another $50,000 was paid for that, to start a congressional investigation of Ernie Green through the House Small Business Committee," he said.

Shorten said he "cut a check" for $50,000 that Clarence Mitchell took, but said he did not know if the Green probe was ever begun.

In later testimony today, Stephen W. Denlinger, former president of the Latin American Manufacturers Association, said that Parren Mitchell told him in early August 1984 that the committee probe of Wedtech was a mere formality in answer to a complaint Mitchell had received about the firm from yet another competitor.

Denlinger, who pleaded guilty two weeks ago to a charge of illegally supplementing the income of a federal official, testified in a plea bargain with prosecutors.

The defense contends the Mitchell brothers were paid to do legitimate lobbying for Wedtech.