Michael Dukakis gave in to Jesse Jackson Saturday on changing Democratic rules for the 1992 delegate selection process, but he stood firm on keeping the party's platform short and non-specific.

Meanwhile, Vice President George Bush savored a victory in Iowa, where his campaign had been sent into a spin by his third-place finish in the caucuses back in February.Jackson hailed the proposed rules changes as "a victory for the people . . . a victory for democracy."

If the rules changes, approved Saturday in Washington by the party's Rules Committee, are adopted by the national convention next month, the number of "super delegates" to the 1992 convention would be cut nearly in half. In addition, all states would be compelled to award delegates to presidential candidates in proportion to their support in the primaries and caucuses.

Jackson had complained that current provisions for super delegates and the rules in a few state primaries and caucuses unfairly kept him from getting as many delegates as he should have.

The rules being changed were the very ones that Dukakis had used to his advantage in clinching the Democratic presidential nomination. The Democrats' Platform Committee, meeting in Denver, was winding up work on a statement of party principles that Michigan Gov. James Blanchard, the committee chairman, said would be short enough to print on a poster and mail out. A 4,000-word draft of the document is one-tenth the size of the 1984 platform.

But unlike the Rules Committee, which convened to rubber-stamp the deals worked out in private negotiations between the Jackson and Dukakis campaigns, some debate was expected at the Platform Committee, where Blanchard said some 20 amendments may be offered.

"They're going to offer amendments," said Christopher Edley, issues director for the Dukakis campaign. "We'll just have to vote them down. But I don't think there'll be a lot of heat and fire, acrimony."

The first Jackson amendment, calling for higher taxes and a freeze on Pentagon spending, was defeated 108-44. The committee also rejected a bid by Jackson to double the education budget.

Differences remained over to what extent the platform should spell out party postitions on the budget, nuclear weapons, a tax increase and defense.

Jackson spent Saturday in Puerto Rico, where he tried to pry loose some Dukakis delegates that he said should be his. Jackson won the state's non-binding primary, but Dukakis came away with almost all the delegates, who were picked separately.

Dukakis was taking a breather in his schedule with a weekend on Nantucket Island in Massachusetts. No public events were planned.

Bush spoke by telephone to state GOP convention delegates in Iowa Saturday, saying "the American people are going to see the clearest-cut choice in an election since the McGovern-Nixon race in 1972."