E. Frances Garro, who makes $50,000 a year on her Senate salary, went swimming the other day in the pool she recently had installed in her backyard.

Benjamin H. Firshein, who also is paid $50,000 a year by the Senate, was playing golf the same day.

Ronald Kavulick, whose Senate salary is $47,000, was washing his car.

The government employes were not on vacation nor was it a weekend or holiday. As employes who transcribe the senators' words during debate -- or reporters of debate, as they are known -- they work only when the Senate is in session. Since the Senate and House were in session last year only about half the year, they -- and their counterparts in the House -- enjoy the benefits of what may be one of the choicest jobs in Washington.

The reporters of debate take stenographic or shorthand notes that produce transcripts of the legislative proceedings of the House and Senate. The transcripts run in each day's Congressional Record.

The Senate has eight such reporters, most of whom are paid $50,000 a year. The House also has eight, all of whom are paid $46,000. The annual cost is more than $1 million for salaries of the transcribers and clerks.

Last year, the House was in session 974 hours of a normal 2,080-hour work year not counting vacations. The Senate was in session 1,159 hours. The House held no sessions at all on 80 work days, while the Senate held no sessions on 86 work days.

"We're not required to be here until 11:30 a.m. Monday if the Senate starts at 11:30 a.m. Monday," said G. Russell Walker, the chief debate reporter in the Senate. Walker, who sails his 27-foot boat in his free time, said the reporters of debate may show up for work 45 minutes before a session starts.

One day late last month, only one of the 20 employes of the office of Vivian R. Spitz, chief debate reporter of the House, was at work. The House was not in session that day.

The next Monday, four of the 20 employes were in the office an hour before the House was to open its session. Spitz was not one of them.

At first, Spitz said House reporters of debate work a normal, 40-hour work week since they work six to eight hours beyond the time when the House is in session each day.

Later, she said she had been referring to individual reporters who are assigned on a rotating basis to be in the office when the House is not in session, and to two reporters who stay afterward to check transcripts.

"All 20 employes are here when the session starts and leave when the gavel goes down except for reporters finishing up transcripts," she said.

Some employes of the reporters' office raise questions about the operation. "We are concerned about the taxpayers' dollars and service to the members, but not at the expense of the taxpayers," said Thomas E. Ladd, assistant to the clerk of the House.

He said that although some of the reporters prepare procedural manuals in their spare time, "We feel they should be reporting."

Another employe, a longtime worker in the office, said, "They have a sheet totaling 40 hours a week, but it doesn't mean anything."

To make more efficient use of the reporters' time, the clerk of the House has recommended to the House Administration Committee that they be made part of the same work force as the reporters who record committee debate so they can cover congressional hearings when the House is not in session.

When the reporters are recording debate, their job is demanding. They cannot ask members to slow down or repeat words, and they may have to work into the morning hours during marathon sessions.

They report for only 10 minutes at a time. Then, they are relieved by other reporters and dictate their notes to transcribers. After dictating, they sip coffee and read magazines, returning to the floor 80 minutes later.

This procedures wastes time, says Ira H. Sharp, an owner of Alderson Reporting Co., a commercial reporting firm that prepares transcripts of congressional hearings.

He said a commercial reporting firm could cover floor debates with one reporter, whose notes would be read at 10-minute intervals by transcribers.

Commercial reporting firms charge about $4.50 a page for trnscripts of congressional hearings and pay their reporters about $1.50 a page. Assuming the debate reporters produce at the standard rate of 30 pages to 35 pages per hour, this means Congress pays debate reporters seven times more per page of transcript than the commercial firms pay their reporters.

Still, the commercial firms make an average profit of 10 percent to 13 percent covering hearings, according to a 1977 General Accounting Office report.

Although reporters employed by federal courts may make up to $75,000 a year through sale of copies, the executive branch pays them no more than $20,000 a year. Commercial reporters may make $25,000 a year if they work more than a 40-hour week.

J. Stanley Kimmitt, secretary of the Senate, said debate reporters cannot be compared with others.

"They perform a unique function for a unique institution," he said. He said they must come to work whenever the Senate goes in session and be able to identify 100 members by sight. They must know parliamentary procedure and prepare transcripts as if the correct forms were used, he said. In addition, Kimmitt said, they spend extra time covering caucuses and other special proceedings.

But Walker, the chief debate reporter, said caucus coverage amounts to about 50 hours a year. Garro, a Senate reporter who once reported congressional hearings for a commercial firm, said, "This (working in the Senate) is easy compared to reporting hearings. You can get used to people's speaking style."

Until two years ago, debate reporters in the House were appointed by the speaker, often on the recommendation of powerful members of Congress. Now, they are appointed by the clerk, who requires them to show they can take down 260 words a minute. This compares with a rate of 80 words to 100 words per minute achieved by most secretaries.

Not every reporter spends the free time taking it easy. Edward D. McCoy, who makes $46,000 a year as a House debate reporter, runs a private court reporting company. He figures he took in an extra $10,000 from the company last year.