IN ADDITION to being represented by two U.S. senators of the highest caliber, Republican Charles McC. Mathias Jr. and Democrat Paul S. Sarbanes, voters in Maryland's Fifth and Eighth congressional districts can point with pride to the representation they have had in the House of Representatives over the years. Republicans as well as Democrats from these two districts have won high marks not only for their constituent service but also for their broad range of legislative interests.

The Fifth District: Democrat Gladys Noon Spellman is seeking her fourth term and deserves it. She continues to work vigorously and effectively on behalf of her constituents and others throughout the region. Though Mrs. Spellman is best known for her keen interest in state and local affairs, including the concerns of federal employees, she has earned a reputation on Capitol Hill as a knowledgeable legislator who can focus on national and foreign policy issues as well. Her Republican opponent, Kevin Igoe, is a 30-year-old budget analyst who has never run for office or been active in politics during the five years he has lived here. That is no match against the career of local and congressional public service that Mrs. Spellman brings to the job.

The Eighth District: Perhaps nowhere else this year has there been a more articulate and informed pair of opposing candidates competing for the votes of an equally articulate and informed electorate than the House contest between Democrat Michael D. Barnes and Republican Newton I. Steers in Montgomery County. Two years ago, it was challenger Barnes who unseated first-term congressman Steers in a lively contest; this time, with the roles reversed, the two men are again treating residents to spirited debates night after night on the widest possible range of world and local issues.

Notable differences between the two candidates on substantive economic, social or energy matters are few. As a result, the noisiest campaign squabbling has been over relatively trivial matters, such as whose advertising has been more unfair, which had the worst attendance record in Congress and which was more eager to do time on the House District of Columbia Committee. More interesting have been the discussions of such subjects as SALT negotiations, which Mr. Barnes feels should be resumed as a protective complement to defense spending, and which Mr. Steers thinks should be suspended so long as the Soviet Union remains in Afghanistan; or tuition tax credits, which Mr. Steers favors for parents who select private schools, and which Mr. Barnes opposes. Both candidates recognize the importance that voters in this district attach to constituent service and county-state issues and have records to prove it.

Where Mr. Barnes has emerged the stronger -- and has won the support of a vast range of business, labor and citizen groups throughout the county -- is in terms of vigor, intensity and effectiveness on Capital Hill. In a remarkably short time he has enjoyed unusual success as an advocate for Maryland and Montgomery County in committees and on the House floor. Mr. Barnes has earned a chance to continue his service.

Other congressional contests include the First District race between incumbent Republican Robert E. Bauman and Democrat Roy Dyson, who is challenging Mr. Bauman for the second time. Even before Mr. Bauman's admissions of alcohol and sexual problems, Mr. Dyson, a delegate to the Maryland House, offered voters a moderate alternative -- a more thoughtful legislative approach to state and national questions than the views of the incumbent. In the Fourth District, Republican Rep. Marjorie S. Holt is running for a fifth term on her consistently dismal voting record of opposition to any significant spending unless it is for the military and on her reputation as a year-round campaigner. Her Democratic opponent, James J. Riley, offers an attractive alternative. In the Sixth District, Democratic Rep. Beverly B. Byron has been quick to learn the ropes as a successor to her late husband. Her interest in a wide variety of issues and her swiftly acquired experience should stand Mrs. Byron in good stead against Republican Raymond E. Beck.