Rep. Steny H. Hoyer (D-Md.), the home-grown politician who has risen to one of the most influential leadership posts in Congress, announced his candidacy yesterday for a fifth term in the House of Representatives.

Hoyer's announcement for the 5th Congressional District seat kicked off one of the county's most unorthodox political races: a primary contest pitting the Democratic Party establishment against the Nation of Islam. The Muslims are attempting to galvanize the county's growing and largely disenfranchised minority population.

Speaking to about 2,000 cheering supporters at an outdoor barbecue, Hoyer yesterday played down race as an issue, promising to serve "each and every citizen of Prince George's County. Our growing Afro-American community needs to be represented," Hoyer said. "I feel very strongly that I want to be judged on my record of 24 years of representing all of the people, all of the time, in every way."

Hoyer, 50, dressed in blue jeans and cowboy boots, appeared confident and relaxed as he received the endorsements of the Democratic U.S. Sens. Paul S. Sarbanes (Md.) and Barbara A. Mikulski (Md.), County Executive Parris Glendening and a host of county elected officials.

Democratic leaders in the county, who cite Hoyer's record of constituent service in his district, offer little hope to his challenger, political newcomer Abdul Alim Muhammad, the national spokesman for Nation of Islam leader Louis Farrakhan.

Glendening predicted that Hoyer, elected last year as chairman of the House Democratic Caucus, will win by a landslide largely because of his record of "bringing home the goodies" in federally funded public works projects.

Hoyer already has raised $453,000 for the campaign, leading all local House members. The total includes $138,000 from political action committees during the last six months of 1989. So far he has no Republican opposition.

But Muhammad's entry into the race is likely to shift the focus of campaign debate away from Hoyer's national stature to local issues such as poverty, drug abuse and crime, party leaders say.

Muhammad, a Washington surgeon who lives in Hillcrest Heights, is the head of Washington operations for the Nation of Islam, which in April 1988 launched its much-touted "Dopebusters" program, designed to drive drug dealers out of housing projects. He also operates a drug treatment clinic, the Abundant Life Clinic, at Paradise Manor in Northeast Washington.

For Hoyer, the race also poses his last election test before district lines are redrawn by the state legislature to reflect new population figures from the 1990 Census. The redistricting could change the shape of Hoyer's district, which now encompasses most of Prince George's County and represents 527,639 people, including a black population of about 45 percent.

Early census estimates indicate that the county's black population has risen sharply since 1980. That could lead to the creation of a new inner-Beltway district with a majority black population. Hoyer's district might then be pushed farther from Washington and include a smaller percentage of black residents.

State Senate President Thomas V. Mike Miller Jr., a longtime Hoyer supporter, said Hoyer has worked ardently to deliver constituent services to the county's black communities, which have formed an important base of his support.

When Hoyer first ran for public office as a state Senate candidate in 1966, "he campaigned extensively in the black communities and was welcomed and supported by blacks at that time," Miller said. "It was largely through their support that Steny was elected, and he has never forgotten that support."

"Steny Hoyer has had an outstanding record of service to blacks," said state Del. Sylvania W. Woods Jr., who intends to run on Hoyer's slate. "Dr. Muhammad will bring up points that need to be made, but I feel very comfortable taking a position with Hoyer in this race."

Glendening credited Hoyer, who sits on the House Appropriations Committee, with securing federal funds for important improvements in the county's transportation network.

Hoyer was instrumental in winning congressional support for funding of the Metrorail system, including planned routes through some of the area's poorest neighborhoods. "The Green Line, worth $685 million, you wouldn't have that without Steny Hoyer," Glendening said. "One year, when he had successfully gotten $200 million for various projects, I asked him, 'Well, Steny, what are you going to do next year?' The next year he got us $300 million, then $325 million," Glendening said.

Hoyer's most recent legislative victory was the passage last month of a federal disabilities bill guaranteeing greater employment opportunities and access to public accommodations for the handicapped.