The happiest general in the Pentagon these days has to be Lt. Gen. Emmett H. Walker Jr., head of the National Guard.

"The Guard's readiness today is the best it has been in its 347-year history," said Walker during an interview in his second-floor Pentagon office.

The reason that's happened is a story of converging interests, both military and political.

The generals running the active duty Army and Air Force long have recognized that there is no way they alone can cover all the world's trouble spots their civilian superiors have declared of strategic interest to the United States. So the war plans call for the Army National Guard, Air National Guard and reserve outfits to fill the gaps.

Walker said he doubts if the public realizes how dependent the active services are on the Guard under what the Pentagon calls "the total force" concept:

* "The Army Guard represents 46 percent of the combat power of the total Army and 37 percent of the support troops.

* "The Air National Guard represents 66 percent of the air defense capability of the Air Force, 54 percent of the tactical reconnaissance forces and 70 percent of the combat communications of the Air Force."

Despite these and other statistics, the Guard often has been a stepchild to the active duty forces when it came to dividing up first-line weapons such as tanks, planes, artillery or even radios.

But the confidence in the Guard that was lost in the 1950s, '60s and early '70s seems to have been regained. Lawmakers for the past several years have insisted that the Air and Army National guards receive first-line equipment, not hand-me-downs of the past. And when the House Armed Services Committee marked up the Defense Department's fiscal 1984 authorization bill, it went beyond hardware and gave the Guard special treatment in manpower.

While freezing the active duty Army, Navy, Air Force and Marine Corps at their current levels, the House committee said the Army National Guard could grow beyond what President Reagan had requested. He sought to increase it from an average strength of 407,400 troops in fiscal 1983 to 418,400 in 1984, but the committee added 6,600, bringing it up to 425,000.

Chairman Les Aspin (D-Wis.) said his House military personnel subcommittee recommended freezing the active-duty services to force the Pentagon to take a serious look at how to make better use of the Guard and other reserves. He said Congress, if not the Pentagon, realizes that the United States does not have enough active-duty forces to cover Europe and the Persian Gulf if simultaneous wars should break out.

Aspin said Congress is demanding that the Pentagon consider organizing the Guard and reserves to fill the gaps widened by the commitment to protect Persian Gulf oil fields.

Pentagon officials, Aspin complained, "produced a manpower report that was just awful" when it came to explaining the role of the reserves. "They haven't seriously looked at it," he said. Aspin said his subcommittee will hold hearings soon to force the Pentagon to address the reserve issue in depth.

But how come that bastion of Pentagon support, the House Armed Services Committee, slapped its old friend this year and clamped a lid on the size of the Army, Navy, Air Force and Marine Corps? Again, interests coverged, as Aspin explained in an interview:

"The liberals want to save money; the conservatives would like to get some increase in effectiveness" by making better use of the reserves, "and, of course, the Guard and reserve constituency want anything that would bring them into a more prominent role."

Gen. Walker said the House committee action was a vote of confidence. "I'm bubbling over with excitement. The feeling toward the military is getting better every day out there. Don't tell me about young people being against the military."