Prince George's County Executive Parris Glendening unveiled a $117 million capital bond issue proposal yesterday, most of which would be spent on 29 road projects, including a new Beltway interchange. Glendening called it the "largest ever" county bond issue for the construction of new highways and widening of existing ones.

If approved by voters in November, the bonds will also be used to build a new criminal court complex and 1,000-car garage in Upper Marlboro, the tiny county seat, at a cost of $25 million. The road projects would cost the county $82.4 million.

By spending the proceeds over four or five years, Glendening said at a news conference, increased tax revenue generated by expected growth in the county will be enough to pay the principal and interest on the bonds. "There will be no additional taxes or revenue source needed," Glendening said, to pay for the improvements.

As an extra benefit of the bond issue, Glendening said, about $16 million raised from property taxes in certain special taxing districts can be shifted from road projects to countywide educational needs.

Glendening earlier promised to spend $40 million more this year for the county school system, including the magnet school programs designed to end a desegregation suit in the county. That money, he said, would come from the $16 million, $11 million more than originally expected from the state and $15 million from additional property tax revenue.

Glendening said yesterday that because funds are available for the educational programs, no county department will suffer cuts in the budget that he will unveil March 31.

Glendening's news conference came as a new proposal to tax portions of interest received by municipal bond holders was raised in the Senate Finance Committee. Several municipalities postponed bond sales as a result, but it was unclear what effect the measure could have on the Prince George's proposal.

The county executive outlined his bond proposal to County Council members Tuesday night at a $500 dinner at the Mount Airy Plantation restaurant, a restored 18th century manor house near Upper Marlboro.

Glendening said the council members and the county's legislative delegation in Annapolis, whom he briefed yesterday morning, were enthusiastic. "There is substantial support for the road system wherever we go," he said.

The proposals cover "almost every area of the county, so the political feedback should be positive," he said. "No project is controversial. All enjoy substantial support and have been on the books for some time."

Using maps strung around a conference room in the county administration building, Glendening pointed out the road projects in what he said are areas of "tremendous growth" between Laurel and Beltsville, around to Greenbelt and Bowie and in the south county areas near Largo and Oxon Hill.

Glendening said there would be only minimal displacement of houses and businesses. "Most are on reserved rights-of-way," he said.

Among the projects planned is a new Beltway intersection between the Capital Centre exit at Central Avenue and the Rte. 4 exit. The proposed new interchange at Ritchie-Marlboro Road is in an area that Glendening said has undergone "tremendous growth" with no Beltway access.

In Laurel-Beltsville, Glendening said, U.S. Rte. 1 has been unable to absorb the growth. A new parallel road will help, he said.

"You've got to build ahead of development," Glendening said, contrasting his program to that of Montgomery County, where officials are trying to build new roads to serve already developed areas. "It's very expensive, complex and politically difficult if you allow growth without these roads in place."

In both counties, the governments are spending county funds to improve state roads and using such arrangements to obtain more highway money for these and other projects from the state.

In Prince George's, the issue proceeds are expected to make available an additional $44 million in matching state funds for the road projects.

Glendening said the bond proceeds, when added to present state and county road programs, would bring the county's highway program to more than $800 million, third largest in Maryland, after Montgomery and Anne Arundel counties.

Other projects to be built with the bond proceeds include the court complex, which would include eight new courtrooms, $4.6 million for fire department facility improvements, $410,000 to plan a north county health center, $3.6 million to expand the Laurel Library and build a new library in the Largo-Kettering area, and $1.5 million as the county's contribution to Metro to purchase new buses to serve the region. P.G. Bond Issue

Here's how the $117.3 million would be spent:

*Roads and bridges, $82.4 million.

*Criminal court facilities, $25 million.

*Health facility planning. $.4 million.

*Libraries, $3.6 million.

*Metrobuses, $1.5 million.

*Fire department facility improvements, $4.6 million.