When President Reagan begins a series of meetings with his Cabinet secretaries today to hammer out the unresolved issues in the fiscal 1983 budget, there will be a longer agenda than any president has faced in recent years.

Office of Management and Budget careerists say this first truly original Reagan budget has become so controversial--especially in the domestic area--that they have been unable or unwilling to cut their usual deals with the departments on smaller issues while leaving only the large ones for the president and the secretary.

That is because so much money has already been taken from domestic programs that further cuts amount to policy decisions instead of the simple funding-level questions that can often be worked out in the old-boy network of budget division directors and their counterparts in the agencies.

While the budget process is generally on schedule, the number of unresolved issues means that much of the work on budget documents and backup papers that normally would be done by this time of year has not been completed.

"By now, we would usually be down to the eight or nine really tough issues for a department that would have to be decided by the secretary, the director and maybe the president, and we would have disposed of 80 or 90 other issues . . . ," a division chief said. "There are still 80 or 90 issues on the table. I think it's because nobody here on OMB's policy side is willing to be reasonable."

Many of those issues were resolved--or will be--in meetings this week and next between the secretary and Budget Review Board (consisting of budget director David A. Stockman, presidential counselor Edwin Meese III and chief of staff James A. Baker III). But many issues will have to be taken to the president.

"However," another OMB careerist cautioned, "that doesn't mean we're all that far behind, because these guys decide things in a hurry once they get to it. I don't know of any real molasses in the system."

Stockman's problems in mid-November over quotations published in the Atlantic Monthly "didn't slow us down for more than a day or two," another careerist said. "He has enormous energy and was able to deal with that and keep the process on course."

By law, the budget must be presented to Congress 15 calendar days after Congress convenes in January. Since Congress now plans to convene Jan. 25, that would make the mandatory submission date Feb. 9, but the final schedule has not been set.

OMB has been working toward publishing the budget on Jan. 18, but that deadline will undoubtedly slide, according to spokesman Edwin L. Dale Jr. As a practical matter, the budget must be completed at least several days in advance of the official date so it can be printed.

The Government Printing Office, which produces the four volumes that make up the Budget of the United States Government, reports that some material for the budget books arrived as early as Nov. 19. But final numbers for the all-important tables that tell people what is really happening to their favorite programs cannot be plugged in until the president decides whether to go with Stockman's cuts, accept a secretary's appeal or order a compromise.

OMB officials say that the delay in the fiscal 1983 budget is in no way releated to the seemingly unending number of fiscal 1982 budgets they had to prepare or massage. In addition to the original Carter budget and four official Reagan modifications, there was substantial OMB staff work in the wrangling over the budget reconciliation bill in July and the continuing resolution two weeks ago. It appears that the 1982 budget will finally be put to rest before Dec. 15, the expiration date for the continuing resolution under which the government is now operating.

OMB's political appointees, who have to make the final decisions, have been impressed with the career staff. "They are precisely what professionals ought to be," a top-level political appointee said. "This is a place of enormous discretion. People state their views internally, then accept the political decision-making process."

Stockman is "giving some thought," Dale said, to adding a fifth volume to the fiscal 1983 budget. The four traditional volumes are the budget itself, the appendix (a more detailed presentation), the budget in brief (just what it says), and the special analyses (which deal extensively with a small number of issues). The fifth volume would contain additional details, with justification for some of the many cuts being contemplated.