When freshman members of the 98th Congress arrived in town in January for their new jobs they received a startling message from House counsel Stanley M. Brand.

"Welcome to Congress," he said. "You can now be sued for libel, defamation of character, employment discrimination and constituent complaints.

"The good news," he said after a pause, "is you have a fully funded, aggressive legal defense counsel."

Brand, 34, received an unusual dose of public attention during the recent battles between five House subcommittees and the Environmental Protection Agency. But as chief attorney for 435 House members, Brand plays a key backstage role in dozens of important legal disputes on Capitol Hill.

His crowded caseload, as he warned the freshmen, contains a growing number of libel and damage suits against members of Congress and their staffs.

An insurance agent has sued staff members on the House Aging Committee for conducting an undercover investigation into the sale of insurance policies to the elderly. Firestone Tire and Rubber Co. tried to compel a congressman's testimony after his subcommittee looked into reports of defects in Firestone 500 tires. Other House staff members have been named as defendants for providing information to newspapers.

"It has a terrible chilling impact on this place," Brand said of the lawsuits. "People are more reserved about what they say and do. They are not as effective, quite frankly, because they're worried about being sued. It's great to call a big hearing and get under the klieg lights, but you have to go into the field to get real information."

The Constitution protects members from liability for anything they say on the floor, but they lose that immunity if they make the same statement to reporters in front of the Rayburn House Office Building. A scientist sued Sen. William Proxmire (D-Wis.) for giving him a "Golden Fleece" award for the scientist's research into why monkeys clench their jaws, a case that ended with an out-of-court settlement.

The issue has become so sensitive, Brand said, that some House members now check with him before making a controversial statement. "I tell them, 'Make it on the floor, don't repeat it and if someone asks you about it, don't talk about it.' The fiction the courts engage in is that speaking to the press is not part of the official process," Brand said.

All this is quite a handful for a "self-taught litigator" from New York. In 1976, Brand was comfortably ensconced at the Securities and Exchange Commission, gradually preparing to join the ranks of the corporate lawyers on K Street, when the House clerk asked him to take the counsel's job.

Although Brand had enjoyed his stint on the Hill in the early 1970s, when he worked for then-Majority Leader Thomas P. (Tip) O'Neill Jr. (D-Mass.) while going to Georgetown Law School at night, the counsel's post did not seem very stimulating.

"It sounded like a big, high-paying job with a big title and a lot of exposure, but not that much going on," Brand said. But he said his wife talked him into it.

"To my amazement, I found we were really not representing members on a consistent basis. Members who were sued had to go to a friend, or to the Justice Department, or get a contract for an outside lawyer."

When the House clerk was sued during a holiday recess, Brand, who had never been in court before, got the case thrown out. "I said, 'Gee, this isn't so hard. Why are we paying lawyers $150 an hour for this stuff?' "

Brand hired two assistants and soon took over most of the House suits, which have proliferated as the courts have become more reluctant to block cases on the grounds of congressional immunity.

He doesn't always get to wear the white hat, however. Sometimes Brand defends members in sex or race discrimination suits filed by employes. There was a spate of these after the courts upheld the former administrative assistant of then-Rep. Otto E. Passman (D-La.), who was fired because the congressman decided he wanted a man for the job.

On other occasions, Brand defends in suits by constituents who say their legislator was negligent in getting them disability benefits or a lost Social Security check. And when the House vetoed a Federal Trade Commission rule on used-car sales practices, Brand had to fight a consumer lawsuit that challenged the legislature's power to block executive branch regulations. He lost before an appeals court, but has asked the Supreme Court to review the decision.

Although Brand thrives on the long hours and endless demands, even he wasn't prepared for the intensity of the EPA controversy. He testified at hearings, negotiated with the Justice Department and finally advised the House to sue for the subpoenaed documents that former EPA administrator Anne M. Burford was withholding. He recalls the exact tally: 259 members voted to hold Burford in contempt of Congress.

"I knew we would get the documents when I saw the groundswell on the floor," he said. "I felt I was part of one of the great moments in congressional history, and that it was based on legal advice I had rendered."

Although he got his $67,500-a-year job through the Democrats, Brand likes to point out that he was equally diligent in pursuing a similar contempt case against President Carter's energy secretary, Charles Duncan. "Some of my best clients are Republicans," he said.

After seven years, Brand occasionally grows frustrated that his House salary "is about two-thirds less than what the lawyers downtown get for doing the same thing I do. But there's no law firm or legal practice in the country that has this kind of caseload in terms of the breadth of legal and constitutional issues. I've got a unique client."