House Democrats are likely to approve some disciplinary measures aimed at enforcing party loyalty when they caucus today in their biannual encounter group, a closed-door meeting at which they decide the rules of the game.

The most dramatic move, the expected expulsion of Phil Gramm (D-Tex.) from the Budget Committee to punish him for supporting President Reagan's program, will not occur until next month when Democrats vote on committee assignments.

However, the three-day caucus this week is expected to fend off a move by southern conservatives to make the Gramm vote a public, rather than secret, ballot.

The caucus is expected to approve a new rule under which a member automatically loses a party-appointed committee seat if he switches political parties in mid-Congress.

The move is aimed at preventing a situation such as that involving Eugene V. Atkinson (Pa.) who became a Republican but held his Democratic seat on the Public Works Committee.

Democrats grumbled this year when Berkley W. Bedell (D-Iowa) made a television commercial endorsing Thomas B. Evans Jr. (R-Del.) over his Democratic opponent.

Likewise, Bob Edgar (D-Pa.), got in trouble for helping Claudine Schneider (R-R.I.), his co-chair of the Northeast-Midwest Coalition.

A rule change making it "a policy of the caucus" that Democrats not support Republicans for federal office is expected to pass but with no specific enforcement provision.

In a more substantive vein, Democratic leaders are supporting a seemingly innocuous parliamentary change that could have long-range consequences.

The change would make it more difficult for the House to pass "riders" on appropriations bills, by making a motion to "rise," in other words, cut off amendments, in order before any riders can be introduced.

This would make it harder for such conservative issues as abortion and busing restrictions to be attached to money bills but would also have made it more difficult to pass an anti-Vietnam war rider, as was done in the 1970s.

A threatened rebellion by powerful committee chairmen against the growing power of the Budget Committee was rumored last week but is unlikely to materialize because Democratic leaders adamantly insist that reforms in the budget process be postponed until a task force headed by Anthony C. Beilenson (D-Calif.) reports early next year.

The chairmen of the committees on Education and Labor, Energy and Commerce, Public Works and Transportation, Post Office and Civil Service, Banking, Finance and Urban Affairs and Foreign Affairs circulated a letter last week with seven proposals to make the budget process more "orderly."

However, Budget Committee Chairman James R. Jones (D-Okla.) worked feverishly to protect his turf against committee chairmen making such proposals as allowing appropriations bills to be passed before the budget resolution establishes ceilings.

They also wanted to make cuts mandatory only on the basis of total committee funding, not on the basis of individual programs, which would make it difficult to keep track of whether Congress is spending more than is budgeted.

To fend off such far-reaching items, a Rules Committee task force headed by Martin Frost (D-Tex.) will recommend, among 20 rules changes, several technical amendments sought by committee chairmen. They include one to require the budget resolution to include economic assumptions.

Another major package of changes that would strengthen the Budget Committee's control is to be brought up in the caucus by David R. Obey (D-Wis.), who said he expects to debate the issues without pressing for votes before the Beilenson report.

Democratic leaders are considering a proposal to extend terms on the Budget Committee from three years to four years and, if the caucus approves that, whether to grandfather in three members, including the influential and prickly Obey whose term expires this year.

Fierce lobbying for positions on Budget, Ways and Means, Appropriations, Energy and Commerce and other committees took place last week as Democratic leaders met with prospective candidates. Blacks are pushing William H. Gray III (D-Pa.) for a Budget seat, and other candidates include Geraldine A. Ferraro (D-N.Y.), Vic Fazio (D-Calif.) and Howard Wolpe (D-Mich.).

Republicans also caucus this week, but "it should be pretty boring," one leadership staffer said. The only contest is for chairman of the Republican Research Committee. James G. Martin (N.C.) is favored to win over Ed Bethune (Ark.)