President Reagan and his senior advisers have instituted a weekly Monday "issues luncheon" to coordinate White House policy making.

The Monday lunches were started about a month ago as a forum for discussions of the status of policy issues, particularly those on which the president faces a decision during the week, according to participants.

The luncheons help prepare Reagan each week, but they are not simply briefings for the president, one White House official said.

Although they are an opportunity for senior White House advisers to update Reagan on various issues, this official said, the sessions also enable him to outline his thinking on current issues.

The luncheons are the only fixed time on the president's weekly schedule when the whole array of current issues is on the agenda before him.

The luncheons are intended to include issues that need presidential attention soon, but they are not decision-making meetings. Decisions are reached after meetings of the Cabinet or its subgroups called Cabinet councils.

In their assessments of the administration's first year, the president and his advisers have stressed that they are pleased with the way Cabinet government has worked.

The full Cabinet met 20 times this year, and Reagan said in a recent interview, "We are going to continue with that system of government." The president is fond of comparing the system to a corporate board of directors, the difference being that "we don't take a vote."

Reagan describes his Cabinet government system in these terms: "When I have heard enough to make a decision, I know that I have to make a decision."

The Monday lunches, however, are an attempt better to organize the president's approach to issues at the start of each week and make sure various senior White House advisers know the range of issues confronting Reagan.

The lunches are attended by Vice President Bush and Reagan's three top advisers-counselor Edwin Meese III, chief of staff James A. Baker III and deputy chief of staff Michael K. Deaver.

Other regular participants are presidential assistants Richard Darman and Craig Fuller, White House communications director David Gergen, domestic policy adviser Martin Anderson and acting national security adviser Adm. James Nance.

There was no issues lunch today because the president is vacationing in southern California. He traveled by helicopter this morning from Los Angeles to his ranch in the mountains above Santa Barbara for a day outdoors before returning to his Los Angeles hotel suite for dinner with his wife and other family members.

The major issue confronting Reagan during his one-week vacation is what further response to make to the crackdown in Poland. A presidential decision on new economic or political steps is expected to be announced in Los Angeles before Reagan departs for Palm Springs Wednesday.