The Joint Chiefs of Staff will decide within the next four to six weeks whether to recommend the creation of a unified, four-service command for military activities in space, according to top Air Force officials who are pushing the idea.

The unified command would coordinate all space activities for the Air Force, Army, Navy and Marines, reflecting the growing importance of space for U.S. military endeavors. There are five such unified commands now, none led by the Air Force.

However, the Navy opposes the proposal and plans to create its own Space Command in Dahlgren, Va., on Oct. 1. The interservice rivalry on the issue reflects traditional competition for defense dollars as well as differing priorities of how space should be used.

A recommendation by the Joint Chiefs for a new unified command, to be located in Colorado Springs, would carry considerable weight with Secretary of Defense Caspar W. Weinberger and President Reagan, who would make the final decision. Reagan's speech last summer urging research into a system, possibly based in space, to defend against nuclear missiles helped spur the Air Force to create its own Space Command in Colorado last fall.

That command has assumed control of the Pentagon's most significant space programs, including development of an anti-satellite weapon, military uses of the space shuttle and much of the research into laser weapons and other high-technology tools that eventually might be used in space or against space vehicles.

The Air Force command also is building a satellite control center that will function as a military equivalent to NASA's Johnson Space Center.

If the Air Force command is expanded into a four-service operation, which Army officials have said they support, the Air Force commanding general also would control the Army's ballistic missile defense group, now based in Huntsville, Ala.

In addition, the unified Space Command would control the satellites that provide navigational aid and weather information to Navy ships.

Navy officials fear that their need for satellite information then would take second place to the Air Force's desire to develop "Star Wars" weaponry.

"We don't want to have to sit around saying, 'Get off the phone, we need to make a long-distance call,' " a Navy official said yesterday.

A senior Air Force official, who asked not to be named, criticized the Navy for what he said is a short-sighted view.

The official said a unified command would help all the services get more funds for space activities.

"Let's say 10 years from now, we have an ASAT anti-satellite capability," the official said. "The Navy will certainly want a say in fleet defense against those satellites that are threatening their ships."

The official also suggested that Chief of Naval Operations Adm. James D. Watkins does not share Navy Secretary John F. Lehman Jr.'s opposition to a unified command.

But a Navy spokesmen said the two men agree that a unified operation is premature and Lehman has proved himself a skilled bureaucratic infighter in past controversies.

Existing unified commands include the Pacific and Atlantic commands, led by the Navy, and three led by Army generals: the European Command in Germany, the Southern Command in Panama and the Readiness Command in Florida.