Del. Stewart Bainum sponsored a bill during the last Maryland General Assembly session to "decouple" the state's corporate taxes from the federal tax code. That bill died in a committee chaired by Sen. Laurence Levitan.

Del. Marilyn Goldwater cosponsored a bill requiring tough new penalties for illegal handgun users. That bill died in a committee chaired by Del. Joseph E. Owens.

Such are the conflicts that typically make for good election-year political combat. But this year in Montgomery County, where the Democratic incumbents, including these four, have teamed up on a slate called "Democrats For '82," those past differences have been all but buried in the name of unity and self-preservation.

"We have a variety of candidates who bring a variety of philosophies (from) within the Democratic party," slate coordinator Patricia Billings said last week. "We had no litmus test (of issues)."

It is precisely that mix of philosophies that upsets party outsiders. They charge that the incumbents' slate lacks philosophical direction and purpose. They accuse liberals on the slate of selling out their principles. Some have banded together to form their own slate--"Democrats for the '80s"--under the banner of the liberal Alliance For Democratic Reform (ADR). The new slate touts itself as the true keeper of the county's liberal Democratic creed.

Calling ADR "the heart and conscience of the Democratic party in Montgomery County," group president Mindy G. Farber last week told an audience: "Our common denominator is our desire to speak out on the issues. . . . The only thing that unites the other slate is incumbency. They have no united positions."

At a time when some politicians see the county becoming more conservative, particularly in the face of shrinking fiscal resources and an increase in urban-style problems, the ADR slate is unabashed at calling itself "liberal." "We have an overlying liberal philosophy," said delegate candidate Daniel A. Borges. "We all accept the label of being liberal or progressive."

So the ADR slate has embraced a broad spectrum of "liberal" issues, including the decoupling of Maryland corporate taxes, tougher penalties for illegal handgun users and continued state funding of Medicaid abortions. They have challenged the incumbents to come up with a similar issues platform.

The "incumbents' slate" idea first developed this year as an alternative to the traditional preprimary Democratic convention. Since 1966, the Democratic party always has held a convention to select an official slate for primary elections, and traditionally those left off the slate have complained that conventions, and slating, were inherently evil.

But some Montgomery County politicians who are now considered "established" remember that, had they not won convention endorsements as newcomers in the last decade, they never would have won their first elected office. Among that group are delegates Helen Koss and Donald Robertson.

"A convention gives new candidates an opportunity to test their strength before the primary, with a minimum expenditure of time and money," Robertson said. "This is a very unstructured election year, and I think that's unfortunate."

The incumbents also questioned the ADR slate's calling itself "liberal." They point to well-known incumbents with impeccable liberal credentials who never have been endorsed by ADR. Koss said the battle between the ADR dissidents and the established incumbents is mostly over procedure, not policy.

This party warfare may bring a sense of deja vu to politicians in Montgomery, where "Ins" battling "Outs" is a way of life. The same split, with many of the same characters, occurred during the 1978 election campaign, when Democratic party dissidents decided to retaliate against the preprimary convention of Democratic incumbents and precinct workers to nominate slate candidates.

The convention, according to its backer, then-party chairman Jim Doherty, was to produce "knowledgeable" endorsements by party activists. But the outsiders, led by losing 1976 congressional candidate Lanny Davis, argued that such a convention was "undemocratic" and would favor incumbents. The Davis outsiders formed their own group, called the "Democratic Coalition," comprising seven dissident factions, including the ADR.

In that year, too, it was the outsiders who argued that Democratic candidates should be held accountable to some kind of issues platform. Doherty and the insiders (meaning incumbents) opposed the platform idea as too rigid and monolithic.

Political history in the county has shown it is always the outsiders who can afford the luxury of running on issues and ideological purity. As incumbents' slate coordinator Billings said, the outsiders have never had to vote on specific bills.

Bitter Democratic party feuds ordinarily could allow Republicans to make further inroads into the overwhelmingly Democratic legislative and county political offices. But the GOP this year is involved in its own internal feud between its ideologues and its pragmatists.

Conservatives are to the GOP what liberal dissidents are to the Democrats. The only Republicans to win elected office from Democratic Montgomery County have for the most part been moderate-to-liberal in the Mathias, Gude, Steers tradition. Sen. Howard A. Denis and Del. Constance Morella (who are running for reelection) and Del. Luiz R. Simmons (who is running for county executive) are the primary examples.

All three Republican incumbents, and some moderate GOP challengers, hope to win by appealing to Democrats. But staunch conservatives--the GOP's political "outsiders"--are balking about Republicans who do not embrace Reaganomics and conservative ideals.

Conservatives are trying to take control of the GOP central committee. State GOP chairman Allan Levey is being challenged from the right for a state Senate seat from Potomac.

Even school board member Marian Greenblatt, a conservative, is being challenged from the right by Bethesda engineer Phillip Buford, who doesn't think Greenblatt is conservative enough. "She's perceived as a conservative, but I don't think she is," Buford said. "She's not for total decentralized control."

So the infighting Democrats can find solace this year in knowing that Republicans are hardly more unified. In philosophical battles between pragmatic "Ins" and ideological "Outs," neither party enjoys a monopoly.