Take a longtime Democratic district, add a sudden influx of new, young residents -- many of them Republican -- then toss in the volatile issue of abortion and the result is one of the more interesting primary races in Central Maryland.

The 13th district, which includes eastern and southern Howard County and parts of Prince George's County, is among the fastest-growing in the region and one of the places where Republicans have made some significant gains. The Democratic edge of 1.87 to 1 in 1986 was cut to 1.48 to 1 in 1990 in the district, an increasingly suburban area that includes Laurel.

Party affiliation could play little part in this race, however, if the abortion issue takes precedence in the election, since national polling suggests that abortion is an issue that cuts across party lines. Opinions vary, as well, on how much interest abortion has generated in District 13.

Some argue that neighborhood concerns over truckstop proposals and highway noise are the major issues in a lackluster election year. The district, which includes the Route 1 corridor, has often felt neglected by county officials and has turned to state legislators for help with constituent problems.

In the District 13-B Republican primary, two antiabortion candidates and one abortion-rights supporter are vying for two seats in the House of Delegates. The two incumbents -- William C. Bevan, 62, a retired educator, and Robert J. DiPietro, 55, the former mayor of Laurel -- are Democrats and will face the two Republican winners in the Nov. 6 general election. Both of the incumbents support the right to choose abortion.

The strongest of the Republican candidates, observers say, is Martin G. Madden, who unsuccessfully sought the same seat in 1986. Madden, 41, who owns a Laurel insurance agency, is running on a ticket with political newcomer John S. Morgan, of Laurel, an engineer at the Johns Hopkins Applied Physics Laboratory. Both say they believe a woman should not be able to terminate a pregnancy except in cases of rape, incest or life-threatening illness.

But Morgan and Madden appear to be tempering their position lately by stressing that Maryland residents should be able to set local policy on the controversial issue themselves by means of a statewide referendum.

"Marylanders as a whole should have the final decision," said Madden, of Clarksville. Asked if he is "pro-life," as he has said in the past, Madden said, "I reject all labels."

Morgan, 26, said he wished the General Assembly had approved the referendum proposal worked out by the Senate earlier this year to end an eight-day abortion filibuster -- a complex compromise that would have put the abortion question to a statewide vote.

Meanwhile, the third Republican candidate, Arthur Reynolds, said the referendum approach is "a cop-out -- people elect lawmakers to make laws."

Asked whether a poll conducted for the two antiabortion candidates showed that a majority in the district support abortion rights, Morgan replied: "I don't think our position is going to cost us votes, as long as we're up front about it." He declined to elaborate on the results of the privately commissioned poll, although he acknowledged, "We asked the abortion question several different ways."

Reynolds, 41, a Columbia lawyer, traced his support for abortion rights to the traditional Republican affinity for freedom from government intrusion.

"I am not seeking to be this district's theological leader," Reynolds said.

On other issues: Reynolds favors more open-space acquisition and laws requiring developers to pay for reforestation. He calls for stricter and more specific sentencing guidelines, abolition of parole, the death penalty in certain circumstances, and random drug testing only in certain cases, say, for airline pilots or operators of heavy equipment.

Madden said he supports holding down property taxes; strengthening environmental measures, such as laws protecting "critical areas"; and mandating recycling. Morgan mentioned his support for charging developers "impact fees."

Both stressed their support for ethics legislation approved a year ago in Prince George's County that would have required County Council members to refrain from voting on land-use matters affecting developers who donated money to their campaigns. The law was overturned on appeal.

"It's wrong when the people who get contributions sit in judgment of the people who contribute money to them," Madden said.

In the Senate race for District 13, there is a Democratic primary between incumbent Sen. Thomas M. Yeager and another political newcomer, Michael McGonnigal. Yeager, 53, a salesman from Fulton, has beena member of the Senate since 1983 and supports abortion rights.

McGonnigal, 36, a Laurel lawyer, said he is against abortion.

"I think the state has the right to step in at the ninth week," said McGonnigal, who directs a student-staffed program providing legal help to the elderly at Catholic University. The winner of the primary will face Republican Guy L. Harriman, a supporter of abortion rights, in November.

Yeager, who sits on the Judicial Proceedings Committee, introduced a sweeping package of campaign finance changes during the last legislative session, many of which were rejected as they have been repeatedly in the Senate in past years.

Among the issues McGonnigal emphasizes: comprehensive state medical insurance for catastrophic illness and a system that pays families for day care. He also favors making fathers who are delinquent on their child-support payments take state jobs. Oddly enough, he supports the abolition of the very institution he seeks to join -- the Maryland Senate.

"They created senates, a group of rich guys, to make sure the poor guys in the House don't get out of hand," McGonnigal said. "In Nebraska, they have a unicameral legislature and it works just fine."