Politics in Maryland will enter a new phase with the retirement next year of three of the state's more senior and influential members, Republican Sen. Charles McC. Mathias, Democratic Rep. Parren Mitchell and Republican Rep. Marjorie S. Holt.

The three will be retiring at a time when two of the delegation's rising national stars may be leaving the House: Montgomery County Democrat Michael Barnes, who has become a leading spokesman for his party on Central American issues, plans to run for the Senate, and Democratic Rep. Barbara Mikulski of Baltimore may do the same.

A shift in half of the 10-member delegation could hurt the ability of Maryland to get the money or legislation its residents want.

Maryland has never had the advantage of states such as New York and California, where population alone makes for a formidable voting bloc in Congress. Instead, it has depended heavily on the influence of its senior members -- who have formed friendships with fellow lawmakers over many years in Congress -- and their ability to move into committee chairmanships, normally awarded on the basis of seniority.

The loss of senior members could significantly diminish the clout of Maryland in Congress, says Rep. Steny Hoyer, a Prince George's County Democrat.

"We'll be losing some of our most influential members, some of our most senior members," he said.

"The question is: Who's left?" said Maryland Democrat Rep. Roy Dyson, who represents Eastern and Southern Maryland. "All of us who are left are new people."

None of the Maryland members who currently are expected to run for reelection has been there more than a decade. Democratic Sen. Paul S. Sarbanes was elected in 1976 and Democratic Rep. Beverly Byron, who would be the dean of the House delegation if she were returned, was first elected to the House in 1978. Dyson and Hoyer were elected in 1980 and Rep. Helen D. Bentley (R-Md.) is serving her first term.

None of those five heads any committees or subcommittees.

In contrast, Mathias is chairman of the Rules Committee, Mitchell chairman of the House Small Business Committee, Barnes chairman of Foreign Affairs subcommittee on western hemisphere affairs and Mikulski is chairwoman of the Merchant Marine and Fisheries subcommittee on oceanography.

Most of the work in Congress takes place in committees and subcommittees. Thus the heads wield enormous influence on matters in those jurisdictions and have leverage in negotiating with other members who may have dealings with their committees.

Mitchell used the chairmanship of the Small Business Committee to pass legislation about set-asides on federal contracts for minority business owners. Mitchell's years as chairman of the Congressional Black Caucus also enabled him to build a voting bloc of at least two dozen members.

In the Senate, where Mathias has been popular with colleagues, he has been able to call on his longtime friendships for help on bills, as he did with Sen. Wendell H. Ford (D-Ky.) after the Senate Commerce Committee voted on a bill that would transfer Dulles and National airports from the federal government to a regional authority.

Mathias felt that the bill, passed earlier this year, was unfair to Maryland. Mathias is not a member of the Commerce Committee, but Ford, ranking Democrat on the Rules Committee, is a member. Ford has worked closely with Mathias and agreed to push Mathias' amendments of the airport legislation.

Because Holt is a Republican, she did not chair any committee or subcommittee in the Democrat-controlled House. However, in 13 years she has become a senior member of the House Armed Services Committee and has worked closely with conservative Republicans and Democrats on the committee. From that perch, Holt has been able to look out for many of the military installations and defense projects in Maryland.

Of the members who are not retiring or seeking office elsewhere, Hoyer is expected to emerge as one of the most influential, in large part because of his position on the House Appropriations Committee.

That committee decides where all the money appropriated by Congress is spent. Members on the Appropriations Committee are in a better position to protect programs in their states, and are sought out by other members to fund hometown projects. Hoyer, because of his Appropriations Committee seat, and Mathias were key players in Maryland's long-running battle to get federal funds to dredge the Baltimore Harbor.

But neither Hoyer nor any of his colleagues appear to be gleeful about the impending power vacuum that may enable them to become more powerful within the Maryland congressional delegation. All say the departures mean their tasks next term will probably be more difficult.

"Fifty percent turnover: It's got to be some sort of a record," Dyson said.